Hashtable Constructors

Definition

Namespace:

System.Collections

Assembly:

System.Runtime.dll

Initializes a new instance of the Hashtable class.

Overloads

Hashtable()	Initializes a new, empty instance of the Hashtable class using the default initial capacity, load factor, hash code provider, and comparer.
Hashtable(Int32, Single, IHashCodeProvider, IComparer)	Obsolete. Initializes a new, empty instance of the Hashtable class using the specified initial capacity, load factor, hash code provider, and comparer.
Hashtable(IDictionary, Single, IHashCodeProvider, IComparer)	Obsolete. Initializes a new instance of the Hashtable class by copying the elements from the specified dictionary to the new Hashtable object. The new Hashtable object has an initial capacity equal to the number of elements copied, and uses the specified load factor, hash code provider, and comparer.
Hashtable(Int32, Single, IEqualityComparer)	Initializes a new, empty instance of the Hashtable class using the specified initial capacity, load factor, and IEqualityComparer object.
Hashtable(Int32, IHashCodeProvider, IComparer)	Obsolete. Initializes a new, empty instance of the Hashtable class using the specified initial capacity, hash code provider, comparer, and the default load factor.
Hashtable(IDictionary, Single, IEqualityComparer)	Initializes a new instance of the Hashtable class by copying the elements from the specified dictionary to the new Hashtable object. The new Hashtable object has an initial capacity equal to the number of elements copied, and uses the specified load factor and IEqualityComparer object.
Hashtable(IDictionary, IHashCodeProvider, IComparer)	Obsolete. Initializes a new instance of the Hashtable class by copying the elements from the specified dictionary to the new Hashtable object. The new Hashtable object has an initial capacity equal to the number of elements copied, and uses the default load factor, and the specified hash code provider and comparer. This API is obsolete. For an alternative, see Hashtable(IDictionary, IEqualityComparer).
Hashtable(Int32, Single)	Initializes a new, empty instance of the Hashtable class using the specified initial capacity and load factor, and the default hash code provider and comparer.
Hashtable(SerializationInfo, StreamingContext)	Obsolete. Initializes a new, empty instance of the Hashtable class that is serializable using the specified SerializationInfo and StreamingContext objects.
Hashtable(IHashCodeProvider, IComparer)	Obsolete. Initializes a new, empty instance of the Hashtable class using the default initial capacity and load factor, and the specified hash code provider and comparer.
Hashtable(IDictionary, Single)	Initializes a new instance of the Hashtable class by copying the elements from the specified dictionary to the new Hashtable object. The new Hashtable object has an initial capacity equal to the number of elements copied, and uses the specified load factor, and the default hash code provider and comparer.
Hashtable(IDictionary, IEqualityComparer)	Initializes a new instance of the Hashtable class by copying the elements from the specified dictionary to a new Hashtable object. The new Hashtable object has an initial capacity equal to the number of elements copied, and uses the default load factor and the specified IEqualityComparer object.
Hashtable(Int32)	Initializes a new, empty instance of the Hashtable class using the specified initial capacity, and the default load factor, hash code provider, and comparer.
Hashtable(IEqualityComparer)	Initializes a new, empty instance of the Hashtable class using the default initial capacity and load factor, and the specified IEqualityComparer object.
Hashtable(IDictionary)	Initializes a new instance of the Hashtable class by copying the elements from the specified dictionary to the new Hashtable object. The new Hashtable object has an initial capacity equal to the number of elements copied, and uses the default load factor, hash code provider, and comparer.
Hashtable(Int32, IEqualityComparer)	Initializes a new, empty instance of the Hashtable class using the specified initial capacity and IEqualityComparer, and the default load factor.

Hashtable()

Source:

Hashtable.cs

Initializes a new, empty instance of the Hashtable class using the default initial capacity, load factor, hash code provider, and comparer.

public:
 Hashtable();

public Hashtable ();

Public Sub New ()

Examples

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using namespace System;
using namespace System::Collections;
using namespace System::Globalization;

ref class myComparer : IEqualityComparer
{
public:
    virtual bool Equals(Object^ x, Object^ y) 
    {
        return x->Equals(y);
    }

    virtual int GetHashCode(Object^ obj)
    {
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

ref class myCultureComparer : IEqualityComparer
{
private:
    CaseInsensitiveComparer^ myComparer;

public:
    myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer::DefaultInvariant;
    }

    myCultureComparer(CultureInfo^ myCulture)
    {
        myComparer = gcnew CaseInsensitiveComparer(myCulture);
    }

    virtual bool Equals(Object^ x, Object^ y) 
    {
        if (myComparer->Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    virtual int GetHashCode(Object^ obj)
    {
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

int main()
{
   
   // Create a hash table using the default hash code provider and the default comparer.
   Hashtable^ myHT1 = gcnew Hashtable((IEqualityComparer^)nullptr);
   myHT1->Add( "FIRST", "Hello" );
   myHT1->Add( "SECOND", "World" );
   myHT1->Add( "THIRD", "!" );
   
   // Create a hash table using the specified IEqualityComparer that uses
   // the default Object.Equals to determine equality.
   Hashtable^ myHT2 = gcnew Hashtable(gcnew myComparer());
   myHT2->Add( "FIRST", "Hello" );
   myHT2->Add( "SECOND", "World" );
   myHT2->Add( "THIRD", "!" );
   
   // Create a hash table using a case-insensitive hash code provider and
   // case-insensitive comparer based on the InvariantCulture.
   Hashtable^ myHT3 = gcnew Hashtable(
            CaseInsensitiveHashCodeProvider::DefaultInvariant,
            CaseInsensitiveComparer::DefaultInvariant);
   myHT3->Add( "FIRST", "Hello" );
   myHT3->Add( "SECOND", "World" );
   myHT3->Add( "THIRD", "!" );
   
   // Create a hash table using an IEqualityComparer that is based on
   // the Turkish culture (tr-TR) where "I" is not the uppercase
   // version of "i".
   CultureInfo^ myCul = gcnew CultureInfo("tr-TR");
   Hashtable^ myHT4 = gcnew Hashtable( gcnew myCultureComparer(myCul) );
   myHT4->Add( "FIRST", "Hello" );
   myHT4->Add( "SECOND", "World" );
   myHT4->Add( "THIRD", "!" );
   
   // Search for a key in each hash table.
   Console::WriteLine( "first is in myHT1: {0}", myHT1->ContainsKey( "first" ) );
   Console::WriteLine( "first is in myHT2: {0}", myHT2->ContainsKey( "first" ) );
   Console::WriteLine( "first is in myHT3: {0}", myHT3->ContainsKey( "first" ) );
   Console::WriteLine( "first is in myHT4: {0}", myHT4->ContainsKey( "first" ) );
}

/* 
This code produces the following output.  Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: False
first is in myHT3: True
first is in myHT4: False

*/

using System;
using System.Collections;
using System.Globalization;

class myComparer : IEqualityComparer
{
    public new bool Equals(object x, object y)
    {
        return x.Equals(y);
    }

    public int GetHashCode(object obj)
    {
        return obj.ToString().ToLower().GetHashCode();
    }
}

class myCultureComparer : IEqualityComparer
{
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public myCultureComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    public new bool Equals(object x, object y)
    {
        return myComparer.Compare(x, y) == 0;
    }

    public int GetHashCode(object obj)
    {
        return obj.ToString().ToLower().GetHashCode();
    }
}

public class SamplesHashtable
{

    public static void Main()
    {

        // Create a hash table using the default comparer.
        var myHT1 = new Hashtable();
        myHT1.Add("FIRST", "Hello");
        myHT1.Add("SECOND", "World");
        myHT1.Add("THIRD", "!");

        // Create a hash table using the specified IEqualityComparer that uses
        // the default Object.Equals to determine equality.
        var myHT2 = new Hashtable(new myComparer());
        myHT2.Add("FIRST", "Hello");
        myHT2.Add("SECOND", "World");
        myHT2.Add("THIRD", "!");

        // Create a hash table using a case-insensitive hash code provider and
        // case-insensitive comparer based on the InvariantCulture.
        Hashtable myHT3 = new Hashtable(
            CaseInsensitiveHashCodeProvider.DefaultInvariant,
            CaseInsensitiveComparer.DefaultInvariant);
        myHT3.Add("FIRST", "Hello");
        myHT3.Add("SECOND", "World");
        myHT3.Add("THIRD", "!");

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        var myCul = new CultureInfo("tr-TR");
        var myHT4 = new Hashtable(new myCultureComparer(myCul));
        myHT4.Add("FIRST", "Hello");
        myHT4.Add("SECOND", "World");
        myHT4.Add("THIRD", "!");

        // Search for a key in each hash table.
        Console.WriteLine($"first is in myHT1: {myHT1.ContainsKey("first")}");
        Console.WriteLine($"first is in myHT2: {myHT2.ContainsKey("first")}");
        Console.WriteLine($"first is in myHT3: {myHT3.ContainsKey("first")}");
        Console.WriteLine($"first is in myHT4: {myHT4.ContainsKey("first")}");
    }
}


/*
This code produces the following output.
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: False
first is in myHT3: True
first is in myHT4: False

*/

Imports System.Collections
Imports System.Globalization

Public Class myComparer
    Implements IEqualityComparer
    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        Return x.Equals(y)
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode

        Return obj.ToString().ToLower().GetHashCode()
    End Function

End Class

Public Class myCultureComparer
    Implements IEqualityComparer

    Dim myComparer As CaseInsensitiveComparer

    Public Sub New()
        myComparer = CaseInsensitiveComparer.DefaultInvariant
    End Sub

    Public Sub New(ByVal myCulture As CultureInfo)
        myComparer = New CaseInsensitiveComparer(myCulture)
    End Sub

    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        Return myComparer.Compare(x, y) = 0
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode
        Return obj.ToString().ToLower().GetHashCode()
    End Function
End Class

Public Class SamplesHashtable

    Public Shared Sub Main()

        ' Create a hash table using the default comparer.
        Dim myHT1 As New Hashtable()
        myHT1.Add("FIRST", "Hello")
        myHT1.Add("SECOND", "World")
        myHT1.Add("THIRD", "!")

        ' Create a hash table using the specified IEqualityComparer that uses
        ' the default Object.Equals to determine equality.
        Dim myHT2 As New Hashtable(New myComparer())
        myHT2.Add("FIRST", "Hello")
        myHT2.Add("SECOND", "World")
        myHT2.Add("THIRD", "!")

        ' Create a hash table using a case-insensitive hash code provider and
        ' case-insensitive comparer based on the InvariantCulture.
        Dim myHT3 As New Hashtable( _
            CaseInsensitiveHashCodeProvider.DefaultInvariant, _
            CaseInsensitiveComparer.DefaultInvariant)
        myHT3.Add("FIRST", "Hello")
        myHT3.Add("SECOND", "World")
        myHT3.Add("THIRD", "!")

        ' Create a hash table using an IEqualityComparer that is based on
        ' the Turkish culture (tr-TR) where "I" is not the uppercase
        ' version of "i".
        Dim myCul As New CultureInfo("tr-TR")
        Dim myHT4 As New Hashtable(New myCultureComparer(myCul))
        myHT4.Add("FIRST", "Hello")
        myHT4.Add("SECOND", "World")
        myHT4.Add("THIRD", "!")

        ' Search for a key in each hash table.
        Console.WriteLine($"first is in myHT1: {myHT1.ContainsKey("first")}")
        Console.WriteLine($"first is in myHT2: {myHT2.ContainsKey("first")}")
        Console.WriteLine($"first is in myHT3: {myHT3.ContainsKey("first")}")
        Console.WriteLine($"first is in myHT4: {myHT4.ContainsKey("first")}")

    End Sub

End Class

'This code produces the following output.
'Results vary depending on the system's culture settings.

'first is in myHT1: False
'first is in myHT2: False
'first is in myHT3: True
'first is in myHT4: False

Remarks

A hash table's capacity is used to calculate the optimal number of hash table buckets based on the load factor. Capacity is automatically increased as required.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The hash code provider dispenses hash codes for keys in the Hashtable object. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

This constructor is an O(1) operation.

See also

• GetHashCode()
• Equals(Object)

Hashtable(Int32, Single, IHashCodeProvider, IComparer)

Source:

Hashtable.cs

Caution

This constructor has been deprecated. Use Hashtable(int, float, IEqualityComparer) instead.

Initializes a new, empty instance of the Hashtable class using the specified initial capacity, load factor, hash code provider, and comparer.

public:
 Hashtable(int capacity, float loadFactor, System::Collections::IHashCodeProvider ^ hcp, System::Collections::IComparer ^ comparer);

[System.Obsolete("This constructor has been deprecated. Use Hashtable(int, float, IEqualityComparer) instead.")]
public Hashtable (int capacity, float loadFactor, System.Collections.IHashCodeProvider? hcp, System.Collections.IComparer? comparer);

[<System.Obsolete("This constructor has been deprecated. Use Hashtable(int, float, IEqualityComparer) instead.")>]
new System.Collections.Hashtable : int * single * System.Collections.IHashCodeProvider * System.Collections.IComparer -> System.Collections.Hashtable

Public Sub New (capacity As Integer, loadFactor As Single, hcp As IHashCodeProvider, comparer As IComparer)

Parameters

capacity

Int32

The approximate number of elements that the Hashtable object can initially contain.

loadFactor

Single

A number in the range from 0.1 through 1.0 that is multiplied by the default value which provides the best performance. The result is the maximum ratio of elements to buckets.

hcp

IHashCodeProvider

The IHashCodeProvider object that supplies the hash codes for all keys in the Hashtable.

-or-

null to use the default hash code provider, which is each key's implementation of GetHashCode().

comparer

IComparer

The IComparer object to use to determine whether two keys are equal.

-or-

null to use the default comparer, which is each key's implementation of Equals(Object).

Attributes

ObsoleteAttribute

Exceptions

ArgumentOutOfRangeException

capacity is less than zero.

-or-

loadFactor is less than 0.1.

-or-

loadFactor is greater than 1.0.

Examples

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using namespace System;
using namespace System::Collections;
using namespace System::Globalization;

ref class myCultureComparer : public IEqualityComparer
{
public:
    CaseInsensitiveComparer^ myComparer;

public:
    myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer::DefaultInvariant;
    }

public:
    myCultureComparer(CultureInfo^ myCulture)
    {
        myComparer = gcnew CaseInsensitiveComparer(myCulture);
    }

public:
    virtual bool Equals(Object^ x, Object^ y)
    {
        if (myComparer->Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

public:
    virtual int GetHashCode(Object^ obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

public ref class SamplesHashtable
{

public:
    static void Main()
    {
        // Create a hash table using the default comparer.
        Hashtable^ myHT1 = gcnew Hashtable(3, .8f);
        myHT1->Add("FIRST", "Hello");
        myHT1->Add("SECOND", "World");
        myHT1->Add("THIRD", "!");

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable^ myHT2 = gcnew Hashtable(3, .8f, gcnew myCultureComparer());
        myHT2->Add("FIRST", "Hello");
        myHT2->Add("SECOND", "World");
        myHT2->Add("THIRD", "!");

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo^ myCul = gcnew CultureInfo("tr-TR");
        Hashtable^ myHT3 = gcnew Hashtable(3, .8f, gcnew myCultureComparer(myCul));
        myHT3->Add("FIRST", "Hello");
        myHT3->Add("SECOND", "World");
        myHT3->Add("THIRD", "!");

        // Search for a key in each hash table.
        Console::WriteLine("first is in myHT1: {0}", myHT1->ContainsKey("first"));
        Console::WriteLine("first is in myHT2: {0}", myHT2->ContainsKey("first"));
        Console::WriteLine("first is in myHT3: {0}", myHT3->ContainsKey("first"));

    }
};

int main()
{
    SamplesHashtable::Main();
}

/* 
This code produces the following output.  Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

using System;
using System.Collections;
using System.Globalization;

class myCultureComparer : IEqualityComparer
{
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public myCultureComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    public new bool Equals(object x, object y)
    {
        if (myComparer.Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public int GetHashCode(object obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj.ToString().ToLower().GetHashCode();
    }
}

public class SamplesHashtable
{

    public static void Main()
    {

        // Create a hash table using the default comparer.
        Hashtable myHT1 = new Hashtable(3, .8f);
        myHT1.Add("FIRST", "Hello");
        myHT1.Add("SECOND", "World");
        myHT1.Add("THIRD", "!");

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable myHT2 = new Hashtable(3, .8f, new myCultureComparer());
        myHT2.Add("FIRST", "Hello");
        myHT2.Add("SECOND", "World");
        myHT2.Add("THIRD", "!");

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo myCul = new CultureInfo("tr-TR");
        Hashtable myHT3 = new Hashtable(3, .8f, new myCultureComparer(myCul));

        myHT3.Add("FIRST", "Hello");
        myHT3.Add("SECOND", "World");
        myHT3.Add("THIRD", "!");

        // Search for a key in each hash table.
        Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"));
        Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"));
        Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"));
    }
}


/*
This code produces the following output.
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

Imports System.Collections
Imports System.Globalization

Public Class myCultureComparer
    Implements IEqualityComparer

    Dim myComparer As CaseInsensitiveComparer

    Public Sub New()
        myComparer = CaseInsensitiveComparer.DefaultInvariant
    End Sub

    Public Sub New(ByVal myCulture As CultureInfo)
        myComparer = New CaseInsensitiveComparer(myCulture)
    End Sub

    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        If (myComparer.Compare(x, y) = 0) Then
            Return True
        Else
            Return False
        End If
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode
        Return obj.ToString().ToLower().GetHashCode()
    End Function
End Class

Public Class SamplesHashtable

    Public Shared Sub Main()

        ' Create a hash table using the default comparer.
        Dim myHT1 As New Hashtable(3, System.Convert.ToSingle(0.8))
        myHT1.Add("FIRST", "Hello")
        myHT1.Add("SECOND", "World")
        myHT1.Add("THIRD", "!")

        ' Create a hash table using the specified IEqualityComparer that uses
        ' the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Dim myHT2 As New Hashtable(3, System.Convert.ToSingle(0.8), _
            New myCultureComparer())

        myHT2.Add("FIRST", "Hello")
        myHT2.Add("SECOND", "World")
        myHT2.Add("THIRD", "!")

        ' Create a hash table using an IEqualityComparer that is based on
        ' the Turkish culture (tr-TR) where "I" is not the uppercase
        ' version of "i".
        Dim myCul As New CultureInfo("tr-TR")
        Dim myHT3 As New Hashtable(3, System.Convert.ToSingle(0.8), _
            New myCultureComparer(myCul))

        myHT3.Add("FIRST", "Hello")
        myHT3.Add("SECOND", "World")
        myHT3.Add("THIRD", "!")

        ' Search for a key in each hash table.
        Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"))
        Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"))
        Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"))

    End Sub

End Class


'This code produces the following output.
'Results vary depending on the system's culture settings.
'
'first is in myHT1: False
'first is in myHT2: True
'first is in myHT3: False

Remarks

Specifying the initial capacity eliminates the need to perform a number of resizing operations while adding elements to the Hashtable object. Capacity is automatically increased as required based on the load factor.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption. A load factor of 1.0 is the best balance between speed and size.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The hash code provider dispenses hash codes for keys in the Hashtable. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

The custom hash code provider and the custom comparer enable scenarios such as doing lookups with case-insensitive strings.

This constructor is an O(n) operation, where n is the capacity parameter.

See also

• IHashCodeProvider
• IComparer
• GetHashCode()
• Equals(Object)

Hashtable(IDictionary, Single, IHashCodeProvider, IComparer)

Source:

Hashtable.cs

Caution

This constructor has been deprecated. Use Hashtable(IDictionary, float, IEqualityComparer) instead.

Initializes a new instance of the Hashtable class by copying the elements from the specified dictionary to the new Hashtable object. The new Hashtable object has an initial capacity equal to the number of elements copied, and uses the specified load factor, hash code provider, and comparer.

public:
 Hashtable(System::Collections::IDictionary ^ d, float loadFactor, System::Collections::IHashCodeProvider ^ hcp, System::Collections::IComparer ^ comparer);

[System.Obsolete("This constructor has been deprecated. Use Hashtable(IDictionary, float, IEqualityComparer) instead.")]
public Hashtable (System.Collections.IDictionary d, float loadFactor, System.Collections.IHashCodeProvider? hcp, System.Collections.IComparer? comparer);

[<System.Obsolete("This constructor has been deprecated. Use Hashtable(IDictionary, float, IEqualityComparer) instead.")>]
new System.Collections.Hashtable : System.Collections.IDictionary * single * System.Collections.IHashCodeProvider * System.Collections.IComparer -> System.Collections.Hashtable

Public Sub New (d As IDictionary, loadFactor As Single, hcp As IHashCodeProvider, comparer As IComparer)

Parameters

d

IDictionary

The IDictionary object to copy to a new Hashtable object.

loadFactor

Single

A number in the range from 0.1 through 1.0 that is multiplied by the default value which provides the best performance. The result is the maximum ratio of elements to buckets.

hcp

IHashCodeProvider

The IHashCodeProvider object that supplies the hash codes for all keys in the Hashtable.

-or-

null to use the default hash code provider, which is each key's implementation of GetHashCode().

comparer

IComparer

The IComparer object to use to determine whether two keys are equal.

-or-

null to use the default comparer, which is each key's implementation of Equals(Object).

Attributes

ObsoleteAttribute

Exceptions

ArgumentNullException

d is null.

ArgumentOutOfRangeException

loadFactor is less than 0.1.

-or-

loadFactor is greater than 1.0.

Examples

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using namespace System;
using namespace System::Collections;
using namespace System::Globalization;

ref class myCultureComparer : public IEqualityComparer
{
public:
    CaseInsensitiveComparer^ myComparer;

public:
    myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer::DefaultInvariant;
    }

public:
    myCultureComparer(CultureInfo^ myCulture)
    {
        myComparer = gcnew CaseInsensitiveComparer(myCulture);
    }

public:
    virtual bool Equals(Object^ x, Object^ y)
    {
        if (myComparer->Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

public:
    virtual int GetHashCode(Object^ obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

public ref class SamplesHashtable
{

public:
    static void Main()
    {
       
       // Create the dictionary.
       SortedList^ mySL = gcnew SortedList;
       mySL->Add( "FIRST", "Hello" );
       mySL->Add( "SECOND", "World" );
       mySL->Add( "THIRD", "!" );
       
       // Create a hash table using the default hash code provider and the default comparer.
       Hashtable^ myHT1 = gcnew Hashtable( mySL, .8f );
       
       // Create a hash table using the specified case-insensitive hash code provider and case-insensitive comparer.
       Hashtable^ myHT2 = gcnew Hashtable( mySL, .8f, gcnew myCultureComparer() );
       
       // Create a hash table using the specified KeyComparer.
       // The KeyComparer uses a case-insensitive hash code provider and a case-insensitive comparer,
       // which are based on the Turkish culture (tr-TR), where "I" is not the uppercase version of "i".
       CultureInfo^ myCul = gcnew CultureInfo( "tr-TR" );
       Hashtable^ myHT3 = gcnew Hashtable( mySL, .8f, gcnew myCultureComparer( myCul ) );
       
       // Search for a key in each hash table.
       Console::WriteLine( "first is in myHT1: {0}", myHT1->ContainsKey( "first" ) );
       Console::WriteLine( "first is in myHT2: {0}", myHT2->ContainsKey( "first" ) );
       Console::WriteLine( "first is in myHT3: {0}", myHT3->ContainsKey( "first" ) );
    }
};

int main()
{
    SamplesHashtable::Main();
}

/* 
This code produces the following output.  Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

using System;
using System.Collections;
using System.Globalization;

class myCultureComparer : IEqualityComparer
{
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public myCultureComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    public new bool Equals(object x, object y)
    {
        if (myComparer.Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public int GetHashCode(object obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj.ToString().ToLower().GetHashCode();
    }
}

public class SamplesHashtable
{

    public static void Main()
    {

        // Create the dictionary.
        SortedList mySL = new SortedList();
        mySL.Add("FIRST", "Hello");
        mySL.Add("SECOND", "World");
        mySL.Add("THIRD", "!");

        // Create a hash table using the default comparer.
        Hashtable myHT1 = new Hashtable(mySL, .8f);

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable myHT2 = new Hashtable(mySL, .8f,
            new myCultureComparer());

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo myCul = new CultureInfo("tr-TR");
        Hashtable myHT3 = new Hashtable(mySL, .8f, new myCultureComparer(myCul));

        // Search for a key in each hash table.
        Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"));
        Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"));
        Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"));
    }
}


/*
This code produces the following output.
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

Imports System.Collections
Imports System.Globalization

Public Class myCultureComparer
    Implements IEqualityComparer

    Dim myComparer As CaseInsensitiveComparer

    Public Sub New()
        myComparer = CaseInsensitiveComparer.DefaultInvariant
    End Sub

    Public Sub New(ByVal myCulture As CultureInfo)
        myComparer = New CaseInsensitiveComparer(myCulture)
    End Sub

    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        If (myComparer.Compare(x, y) = 0) Then
            Return True
        Else
            Return False
        End If
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode
        Return obj.ToString().ToLower().GetHashCode()
    End Function
End Class

Public Class SamplesHashtable   

   Public Shared Sub Main()

      ' Create the dictionary.
      Dim mySL As New SortedList()
      mySL.Add("FIRST", "Hello")
      mySL.Add("SECOND", "World")
      mySL.Add("THIRD", "!")

      ' Create a hash table using the default comparer.
      Dim myHT1 As New Hashtable(mySL, System.Convert.ToSingle(0.8))

      ' Create a hash table using the specified IEqualityComparer that uses
      ' the CaseInsensitiveComparer.DefaultInvariant to determine equality.
      Dim myHT2 As New Hashtable(mySL, System.Convert.ToSingle(0.8), _
        New myCultureComparer())

      ' Create a hash table using an IEqualityComparer that is based on
      ' the Turkish culture (tr-TR) where "I" is not the uppercase
      ' version of "i".
      Dim myCul As New CultureInfo("tr-TR")
      Dim myHT3 As New Hashtable(mySL, System.Convert.ToSingle(0.8), _
        New myCultureComparer(myCul))

      ' Search for a key in each hash table.
      Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"))
      Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"))
      Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"))

   End Sub

End Class


'This code produces the following output.
'Results vary depending on the system's culture settings.
'
'first is in myHT1: False
'first is in myHT2: True
'first is in myHT3: False

Remarks

The initial capacity is set to the number of elements in the source dictionary. Capacity is automatically increased as required based on the load factor.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption. A load factor of 1.0 is the best balance between speed and size.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The hash code provider dispenses hash codes for keys in the Hashtable object. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

The custom hash code provider and the custom comparer enable scenarios such as doing lookups with case-insensitive strings.

The elements of the new Hashtable are sorted in the same order in which the enumerator iterates through the IDictionary object.

This constructor is an O(n) operation, where n is the number of elements in the d parameter.

Hashtable(Int32, Single, IEqualityComparer)

Source:

Hashtable.cs

Initializes a new, empty instance of the Hashtable class using the specified initial capacity, load factor, and IEqualityComparer object.

public:
 Hashtable(int capacity, float loadFactor, System::Collections::IEqualityComparer ^ equalityComparer);

public Hashtable (int capacity, float loadFactor, System.Collections.IEqualityComparer? equalityComparer);

new System.Collections.Hashtable : int * single * System.Collections.IEqualityComparer -> System.Collections.Hashtable

Public Sub New (capacity As Integer, loadFactor As Single, equalityComparer As IEqualityComparer)

Parameters

capacity

Int32

The approximate number of elements that the Hashtable object can initially contain.

loadFactor

Single

A number in the range from 0.1 through 1.0 that is multiplied by the default value which provides the best performance. The result is the maximum ratio of elements to buckets.

equalityComparer

IEqualityComparer

The IEqualityComparer object that defines the hash code provider and the comparer to use with the Hashtable.

-or-

null to use the default hash code provider and the default comparer. The default hash code provider is each key's implementation of GetHashCode() and the default comparer is each key's implementation of Equals(Object).

Exceptions

ArgumentOutOfRangeException

capacity is less than zero.

-or-

loadFactor is less than 0.1.

-or-

loadFactor is greater than 1.0.

Examples

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using namespace System;
using namespace System::Collections;
using namespace System::Globalization;

ref class myCultureComparer : public IEqualityComparer
{
public:
    CaseInsensitiveComparer^ myComparer;

public:
    myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer::DefaultInvariant;
    }

public:
    myCultureComparer(CultureInfo^ myCulture)
    {
        myComparer = gcnew CaseInsensitiveComparer(myCulture);
    }

public:
    virtual bool Equals(Object^ x, Object^ y)
    {
        if (myComparer->Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

public:
    virtual int GetHashCode(Object^ obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

public ref class SamplesHashtable
{

public:
    static void Main()
    {
        // Create a hash table using the default comparer.
        Hashtable^ myHT1 = gcnew Hashtable(3, .8f);
        myHT1->Add("FIRST", "Hello");
        myHT1->Add("SECOND", "World");
        myHT1->Add("THIRD", "!");

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable^ myHT2 = gcnew Hashtable(3, .8f, gcnew myCultureComparer());
        myHT2->Add("FIRST", "Hello");
        myHT2->Add("SECOND", "World");
        myHT2->Add("THIRD", "!");

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo^ myCul = gcnew CultureInfo("tr-TR");
        Hashtable^ myHT3 = gcnew Hashtable(3, .8f, gcnew myCultureComparer(myCul));
        myHT3->Add("FIRST", "Hello");
        myHT3->Add("SECOND", "World");
        myHT3->Add("THIRD", "!");

        // Search for a key in each hash table.
        Console::WriteLine("first is in myHT1: {0}", myHT1->ContainsKey("first"));
        Console::WriteLine("first is in myHT2: {0}", myHT2->ContainsKey("first"));
        Console::WriteLine("first is in myHT3: {0}", myHT3->ContainsKey("first"));

    }
};

int main()
{
    SamplesHashtable::Main();
}

/* 
This code produces the following output.  Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

using System;
using System.Collections;
using System.Globalization;

class myCultureComparer : IEqualityComparer
{
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public myCultureComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    public new bool Equals(object x, object y)
    {
        if (myComparer.Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public int GetHashCode(object obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj.ToString().ToLower().GetHashCode();
    }
}

public class SamplesHashtable
{

    public static void Main()
    {

        // Create a hash table using the default comparer.
        Hashtable myHT1 = new Hashtable(3, .8f);
        myHT1.Add("FIRST", "Hello");
        myHT1.Add("SECOND", "World");
        myHT1.Add("THIRD", "!");

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable myHT2 = new Hashtable(3, .8f, new myCultureComparer());
        myHT2.Add("FIRST", "Hello");
        myHT2.Add("SECOND", "World");
        myHT2.Add("THIRD", "!");

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo myCul = new CultureInfo("tr-TR");
        Hashtable myHT3 = new Hashtable(3, .8f, new myCultureComparer(myCul));

        myHT3.Add("FIRST", "Hello");
        myHT3.Add("SECOND", "World");
        myHT3.Add("THIRD", "!");

        // Search for a key in each hash table.
        Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"));
        Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"));
        Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"));
    }
}


/*
This code produces the following output.
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

Imports System.Collections
Imports System.Globalization

Public Class myCultureComparer
    Implements IEqualityComparer

    Dim myComparer As CaseInsensitiveComparer

    Public Sub New()
        myComparer = CaseInsensitiveComparer.DefaultInvariant
    End Sub

    Public Sub New(ByVal myCulture As CultureInfo)
        myComparer = New CaseInsensitiveComparer(myCulture)
    End Sub

    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        If (myComparer.Compare(x, y) = 0) Then
            Return True
        Else
            Return False
        End If
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode
        Return obj.ToString().ToLower().GetHashCode()
    End Function
End Class

Public Class SamplesHashtable

    Public Shared Sub Main()

        ' Create a hash table using the default comparer.
        Dim myHT1 As New Hashtable(3, System.Convert.ToSingle(0.8))
        myHT1.Add("FIRST", "Hello")
        myHT1.Add("SECOND", "World")
        myHT1.Add("THIRD", "!")

        ' Create a hash table using the specified IEqualityComparer that uses
        ' the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Dim myHT2 As New Hashtable(3, System.Convert.ToSingle(0.8), _
            New myCultureComparer())

        myHT2.Add("FIRST", "Hello")
        myHT2.Add("SECOND", "World")
        myHT2.Add("THIRD", "!")

        ' Create a hash table using an IEqualityComparer that is based on
        ' the Turkish culture (tr-TR) where "I" is not the uppercase
        ' version of "i".
        Dim myCul As New CultureInfo("tr-TR")
        Dim myHT3 As New Hashtable(3, System.Convert.ToSingle(0.8), _
            New myCultureComparer(myCul))

        myHT3.Add("FIRST", "Hello")
        myHT3.Add("SECOND", "World")
        myHT3.Add("THIRD", "!")

        ' Search for a key in each hash table.
        Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"))
        Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"))
        Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"))

    End Sub

End Class


'This code produces the following output.
'Results vary depending on the system's culture settings.
'
'first is in myHT1: False
'first is in myHT2: True
'first is in myHT3: False

Remarks

Specifying the initial capacity eliminates the need to perform a number of resizing operations while adding elements to the Hashtable object. Capacity is automatically increased as required based on the load factor.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption. A load factor of 1.0 is the best balance between speed and size.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The IEqualityComparer object includes both the hash code provider and the comparer. If an IEqualityComparer is used in the Hashtable constructor, the objects used as keys in the Hashtable are not required to override the Object.GetHashCode and Object.Equals methods.

The hash code provider dispenses hash codes for keys in the Hashtable. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

The IEqualityComparer enables scenarios such as doing lookups with case-insensitive strings.

This constructor is an O(n) operation, where n is the capacity parameter.

See also

• IEqualityComparer

Hashtable(Int32, IHashCodeProvider, IComparer)

Source:

Hashtable.cs

Caution

This constructor has been deprecated. Use Hashtable(int, IEqualityComparer) instead.

Initializes a new, empty instance of the Hashtable class using the specified initial capacity, hash code provider, comparer, and the default load factor.

public:
 Hashtable(int capacity, System::Collections::IHashCodeProvider ^ hcp, System::Collections::IComparer ^ comparer);

[System.Obsolete("This constructor has been deprecated. Use Hashtable(int, IEqualityComparer) instead.")]
public Hashtable (int capacity, System.Collections.IHashCodeProvider? hcp, System.Collections.IComparer? comparer);

[<System.Obsolete("This constructor has been deprecated. Use Hashtable(int, IEqualityComparer) instead.")>]
new System.Collections.Hashtable : int * System.Collections.IHashCodeProvider * System.Collections.IComparer -> System.Collections.Hashtable

Public Sub New (capacity As Integer, hcp As IHashCodeProvider, comparer As IComparer)

Parameters

capacity

Int32

The approximate number of elements that the Hashtable object can initially contain.

hcp

IHashCodeProvider

The IHashCodeProvider object that supplies the hash codes for all keys in the Hashtable.

-or-

null to use the default hash code provider, which is each key's implementation of GetHashCode().

comparer

IComparer

The IComparer object to use to determine whether two keys are equal.

-or-

null to use the default comparer, which is each key's implementation of Equals(Object).

Attributes

ObsoleteAttribute

Exceptions

ArgumentOutOfRangeException

capacity is less than zero.

Examples

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using namespace System;
using namespace System::Collections;
using namespace System::Globalization;

ref class myCultureComparer : public IEqualityComparer
{
public:
    CaseInsensitiveComparer^ myComparer;

public:
    myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer::DefaultInvariant;
    }

public:
    myCultureComparer(CultureInfo^ myCulture)
    {
        myComparer = gcnew CaseInsensitiveComparer(myCulture);
    }

public:
    virtual bool Equals(Object^ x, Object^ y)
    {
        if (myComparer->Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

public:
    virtual int GetHashCode(Object^ obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

public ref class SamplesHashtable
{

public:
    static void Main()
    {
        // Create a hash table using the default comparer.
        Hashtable^ myHT1 = gcnew Hashtable(3);
        myHT1->Add("FIRST", "Hello");
        myHT1->Add("SECOND", "World");
        myHT1->Add("THIRD", "!");

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable^ myHT2 = gcnew Hashtable(3, gcnew myCultureComparer());
        myHT2->Add("FIRST", "Hello");
        myHT2->Add("SECOND", "World");
        myHT2->Add("THIRD", "!");

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo^ myCul = gcnew CultureInfo("tr-TR");
        Hashtable^ myHT3 = gcnew Hashtable(3, gcnew myCultureComparer(myCul));
        myHT3->Add("FIRST", "Hello");
        myHT3->Add("SECOND", "World");
        myHT3->Add("THIRD", "!");

        // Search for a key in each hash table.
        Console::WriteLine("first is in myHT1: {0}", myHT1->ContainsKey("first"));
        Console::WriteLine("first is in myHT2: {0}", myHT2->ContainsKey("first"));
        Console::WriteLine("first is in myHT3: {0}", myHT3->ContainsKey("first"));

    }
};

int main()
{
    SamplesHashtable::Main();
}

/* 
This code produces the following output.  Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

using System;
using System.Collections;
using System.Globalization;

class myCultureComparer : IEqualityComparer
{
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public myCultureComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    public new bool Equals(object x, object y)
    {
        if (myComparer.Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public int GetHashCode(object obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj.ToString().ToLower().GetHashCode();
    }
}

public class SamplesHashtable
{

    public static void Main()
    {

        // Create a hash table using the default comparer.
        Hashtable myHT1 = new Hashtable(3);
        myHT1.Add("FIRST", "Hello");
        myHT1.Add("SECOND", "World");
        myHT1.Add("THIRD", "!");

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable myHT2 = new Hashtable(3, new myCultureComparer());
        myHT2.Add("FIRST", "Hello");
        myHT2.Add("SECOND", "World");
        myHT2.Add("THIRD", "!");

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo myCul = new CultureInfo("tr-TR");
        Hashtable myHT3 = new Hashtable(3, new myCultureComparer(myCul));
        myHT3.Add("FIRST", "Hello");
        myHT3.Add("SECOND", "World");
        myHT3.Add("THIRD", "!");

        // Search for a key in each hash table.
        Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"));
        Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"));
        Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"));
    }
}


/*
This code produces the following output.
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

Imports System.Collections
Imports System.Globalization

Public Class myCultureComparer
    Implements IEqualityComparer

    Dim myComparer As CaseInsensitiveComparer

    Public Sub New()
        myComparer = CaseInsensitiveComparer.DefaultInvariant
    End Sub

    Public Sub New(ByVal myCulture As CultureInfo)
        myComparer = New CaseInsensitiveComparer(myCulture)
    End Sub

    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        If (myComparer.Compare(x, y) = 0) Then
            Return True
        Else
            Return False
        End If
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode
        Return obj.ToString().ToLower().GetHashCode()
    End Function
End Class

Public Class SamplesHashtable   

   Public Shared Sub Main()

      ' Create a hash table using the default comparer.
      Dim myHT1 As New Hashtable(3)
      myHT1.Add("FIRST", "Hello")
      myHT1.Add("SECOND", "World")
      myHT1.Add("THIRD", "!")

      ' Create a hash table using the specified IEqualityComparer that uses
      ' the CaseInsensitiveComparer.DefaultInvariant to determine equality.
      Dim myHT2 As New Hashtable(3, New myCultureComparer())
      myHT2.Add("FIRST", "Hello")
      myHT2.Add("SECOND", "World")
      myHT2.Add("THIRD", "!")

      ' Create a hash table using an IEqualityComparer that is based on
      ' the Turkish culture (tr-TR) where "I" is not the uppercase
      ' version of "i".
      Dim myCul As New CultureInfo("tr-TR")
      Dim myHT3 As New Hashtable(3, New myCultureComparer(myCul))
      myHT3.Add("FIRST", "Hello")
      myHT3.Add("SECOND", "World")
      myHT3.Add("THIRD", "!")

      ' Search for a key in each hash table.
      Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"))
      Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"))
      Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"))

   End Sub

End Class


'This code produces the following output.
'Results vary depending on the system's culture settings.
'
'first is in myHT1: False
'first is in myHT2: True
'first is in myHT3: False

Remarks

Specifying the initial capacity eliminates the need to perform a number of resizing operations while adding elements to the Hashtable object. Capacity is automatically increased as required based on the load factor.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The hash code provider dispenses hash codes for keys in the Hashtable. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

The custom hash code provider and the custom comparer enable scenarios such as doing lookups with case-insensitive strings.

This constructor is an O(n) operation, where n is the capacity parameter.

See also

• IHashCodeProvider
• IComparer
• GetHashCode()
• Equals(Object)

Hashtable(IDictionary, Single, IEqualityComparer)

Source:

Hashtable.cs

Initializes a new instance of the Hashtable class by copying the elements from the specified dictionary to the new Hashtable object. The new Hashtable object has an initial capacity equal to the number of elements copied, and uses the specified load factor and IEqualityComparer object.

public:
 Hashtable(System::Collections::IDictionary ^ d, float loadFactor, System::Collections::IEqualityComparer ^ equalityComparer);

public Hashtable (System.Collections.IDictionary d, float loadFactor, System.Collections.IEqualityComparer? equalityComparer);

new System.Collections.Hashtable : System.Collections.IDictionary * single * System.Collections.IEqualityComparer -> System.Collections.Hashtable

Public Sub New (d As IDictionary, loadFactor As Single, equalityComparer As IEqualityComparer)

Parameters

d

IDictionary

The IDictionary object to copy to a new Hashtable object.

loadFactor

Single

A number in the range from 0.1 through 1.0 that is multiplied by the default value which provides the best performance. The result is the maximum ratio of elements to buckets.

equalityComparer

IEqualityComparer

The IEqualityComparer object that defines the hash code provider and the comparer to use with the Hashtable.

-or-

null to use the default hash code provider and the default comparer. The default hash code provider is each key's implementation of GetHashCode() and the default comparer is each key's implementation of Equals(Object).

Exceptions

ArgumentNullException

d is null.

ArgumentOutOfRangeException

loadFactor is less than 0.1.

-or-

loadFactor is greater than 1.0.

Examples

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using namespace System;
using namespace System::Collections;
using namespace System::Globalization;

ref class myCultureComparer : public IEqualityComparer
{
public:
    CaseInsensitiveComparer^ myComparer;

public:
    myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer::DefaultInvariant;
    }

public:
    myCultureComparer(CultureInfo^ myCulture)
    {
        myComparer = gcnew CaseInsensitiveComparer(myCulture);
    }

public:
    virtual bool Equals(Object^ x, Object^ y)
    {
        if (myComparer->Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

public:
    virtual int GetHashCode(Object^ obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

public ref class SamplesHashtable
{

public:
    static void Main()
    {
       
       // Create the dictionary.
       SortedList^ mySL = gcnew SortedList;
       mySL->Add( "FIRST", "Hello" );
       mySL->Add( "SECOND", "World" );
       mySL->Add( "THIRD", "!" );
       
       // Create a hash table using the default hash code provider and the default comparer.
       Hashtable^ myHT1 = gcnew Hashtable( mySL, .8f );
       
       // Create a hash table using the specified case-insensitive hash code provider and case-insensitive comparer.
       Hashtable^ myHT2 = gcnew Hashtable( mySL, .8f, gcnew myCultureComparer() );
       
       // Create a hash table using the specified KeyComparer.
       // The KeyComparer uses a case-insensitive hash code provider and a case-insensitive comparer,
       // which are based on the Turkish culture (tr-TR), where "I" is not the uppercase version of "i".
       CultureInfo^ myCul = gcnew CultureInfo( "tr-TR" );
       Hashtable^ myHT3 = gcnew Hashtable( mySL, .8f, gcnew myCultureComparer( myCul ) );
       
       // Search for a key in each hash table.
       Console::WriteLine( "first is in myHT1: {0}", myHT1->ContainsKey( "first" ) );
       Console::WriteLine( "first is in myHT2: {0}", myHT2->ContainsKey( "first" ) );
       Console::WriteLine( "first is in myHT3: {0}", myHT3->ContainsKey( "first" ) );
    }
};

int main()
{
    SamplesHashtable::Main();
}

/* 
This code produces the following output.  Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

using System;
using System.Collections;
using System.Globalization;

class myCultureComparer : IEqualityComparer
{
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public myCultureComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    public new bool Equals(object x, object y)
    {
        if (myComparer.Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public int GetHashCode(object obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj.ToString().ToLower().GetHashCode();
    }
}

public class SamplesHashtable
{

    public static void Main()
    {

        // Create the dictionary.
        SortedList mySL = new SortedList();
        mySL.Add("FIRST", "Hello");
        mySL.Add("SECOND", "World");
        mySL.Add("THIRD", "!");

        // Create a hash table using the default comparer.
        Hashtable myHT1 = new Hashtable(mySL, .8f);

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable myHT2 = new Hashtable(mySL, .8f,
            new myCultureComparer());

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo myCul = new CultureInfo("tr-TR");
        Hashtable myHT3 = new Hashtable(mySL, .8f, new myCultureComparer(myCul));

        // Search for a key in each hash table.
        Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"));
        Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"));
        Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"));
    }
}


/*
This code produces the following output.
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

Imports System.Collections
Imports System.Globalization

Public Class myCultureComparer
    Implements IEqualityComparer

    Dim myComparer As CaseInsensitiveComparer

    Public Sub New()
        myComparer = CaseInsensitiveComparer.DefaultInvariant
    End Sub

    Public Sub New(ByVal myCulture As CultureInfo)
        myComparer = New CaseInsensitiveComparer(myCulture)
    End Sub

    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        If (myComparer.Compare(x, y) = 0) Then
            Return True
        Else
            Return False
        End If
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode
        Return obj.ToString().ToLower().GetHashCode()
    End Function
End Class

Public Class SamplesHashtable   

   Public Shared Sub Main()

      ' Create the dictionary.
      Dim mySL As New SortedList()
      mySL.Add("FIRST", "Hello")
      mySL.Add("SECOND", "World")
      mySL.Add("THIRD", "!")

      ' Create a hash table using the default comparer.
      Dim myHT1 As New Hashtable(mySL, System.Convert.ToSingle(0.8))

      ' Create a hash table using the specified IEqualityComparer that uses
      ' the CaseInsensitiveComparer.DefaultInvariant to determine equality.
      Dim myHT2 As New Hashtable(mySL, System.Convert.ToSingle(0.8), _
        New myCultureComparer())

      ' Create a hash table using an IEqualityComparer that is based on
      ' the Turkish culture (tr-TR) where "I" is not the uppercase
      ' version of "i".
      Dim myCul As New CultureInfo("tr-TR")
      Dim myHT3 As New Hashtable(mySL, System.Convert.ToSingle(0.8), _
        New myCultureComparer(myCul))

      ' Search for a key in each hash table.
      Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"))
      Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"))
      Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"))

   End Sub

End Class


'This code produces the following output.
'Results vary depending on the system's culture settings.
'
'first is in myHT1: False
'first is in myHT2: True
'first is in myHT3: False

Remarks

The initial capacity is set to the number of elements in the source dictionary. Capacity is automatically increased as required based on the load factor.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption. A load factor of 1.0 is the best balance between speed and size.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The IEqualityComparer object includes both the hash code provider and the comparer. If an IEqualityComparer is used in the Hashtable constructor, the objects used as keys in the Hashtable object are not required to override the Object.GetHashCode and Object.Equals methods.

The hash code provider dispenses hash codes for keys in the Hashtable. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

The IEqualityComparer enables scenarios such as doing lookups with case-insensitive strings.

The elements of the new Hashtable are sorted in the same order in which the enumerator iterates through the IDictionary object.

This constructor is an O(n) operation, where n is the number of elements in the d parameter.

See also

• IEqualityComparer

Hashtable(IDictionary, IHashCodeProvider, IComparer)

Source:

Hashtable.cs

Caution

This constructor has been deprecated. Use Hashtable(IDictionary, IEqualityComparer) instead.

Initializes a new instance of the Hashtable class by copying the elements from the specified dictionary to the new Hashtable object. The new Hashtable object has an initial capacity equal to the number of elements copied, and uses the default load factor, and the specified hash code provider and comparer. This API is obsolete. For an alternative, see Hashtable(IDictionary, IEqualityComparer).

public:
 Hashtable(System::Collections::IDictionary ^ d, System::Collections::IHashCodeProvider ^ hcp, System::Collections::IComparer ^ comparer);

[System.Obsolete("This constructor has been deprecated. Use Hashtable(IDictionary, IEqualityComparer) instead.")]
public Hashtable (System.Collections.IDictionary d, System.Collections.IHashCodeProvider? hcp, System.Collections.IComparer? comparer);

[<System.Obsolete("This constructor has been deprecated. Use Hashtable(IDictionary, IEqualityComparer) instead.")>]
new System.Collections.Hashtable : System.Collections.IDictionary * System.Collections.IHashCodeProvider * System.Collections.IComparer -> System.Collections.Hashtable

Public Sub New (d As IDictionary, hcp As IHashCodeProvider, comparer As IComparer)

Parameters

d

IDictionary

The IDictionary object to copy to a new Hashtable object.

hcp

IHashCodeProvider

The IHashCodeProvider object that supplies the hash codes for all keys in the Hashtable.

-or-

null to use the default hash code provider, which is each key's implementation of GetHashCode().

comparer

IComparer

The IComparer object to use to determine whether two keys are equal.

-or-

null to use the default comparer, which is each key's implementation of Equals(Object).

Attributes

ObsoleteAttribute

Exceptions

ArgumentNullException

d is null.

Examples

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using namespace System;
using namespace System::Collections;
using namespace System::Globalization;

ref class myCultureComparer : public IEqualityComparer
{
public:
    CaseInsensitiveComparer^ myComparer;

public:
    myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer::DefaultInvariant;
    }

public:
    myCultureComparer(CultureInfo^ myCulture)
    {
        myComparer = gcnew CaseInsensitiveComparer(myCulture);
    }

public:
    virtual bool Equals(Object^ x, Object^ y)
    {
        if (myComparer->Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

public:
    virtual int GetHashCode(Object^ obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

public ref class SamplesHashtable
{

public:
    static void Main()
    {
        // Create the dictionary.
        SortedList^ mySL = gcnew SortedList();
        mySL->Add("FIRST", "Hello");
        mySL->Add("SECOND", "World");
        mySL->Add("THIRD", "!");

        // Create a hash table using the default comparer.
        Hashtable^ myHT1 = gcnew Hashtable(mySL);

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable^ myHT2 = gcnew Hashtable(mySL, gcnew myCultureComparer());

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo^ myCul = gcnew CultureInfo("tr-TR");
        Hashtable^ myHT3 = gcnew Hashtable(mySL, gcnew myCultureComparer(myCul));

        // Search for a key in each hash table.
        Console::WriteLine("first is in myHT1: {0}", myHT1->ContainsKey("first"));
        Console::WriteLine("first is in myHT2: {0}", myHT2->ContainsKey("first"));
        Console::WriteLine("first is in myHT3: {0}", myHT3->ContainsKey("first"));
    }
};

int main()
{
    SamplesHashtable::Main();
};

/* 
This code produces the following output. 
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

using System;
using System.Collections;
using System.Globalization;

class myCultureComparer : IEqualityComparer
{
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public myCultureComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    public new bool Equals(object x, object y)
    {
        return myComparer.Compare(x, y) == 0;
    }

    public int GetHashCode(object obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj.ToString().ToLower().GetHashCode();
    }
}

public class SamplesHashtable
{

    public static void Main()
    {

        // Create the dictionary.
        var mySL = new SortedList();
        mySL.Add("FIRST", "Hello");
        mySL.Add("SECOND", "World");
        mySL.Add("THIRD", "!");

        // Create a hash table using the default comparer.
        var myHT1 = new Hashtable(mySL);

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        var myHT2 = new Hashtable(mySL, new myCultureComparer());

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        var myCul = new CultureInfo("tr-TR");
        var myHT3 = new Hashtable(mySL, new myCultureComparer(myCul));

        // Search for a key in each hash table.
        Console.WriteLine($"first is in myHT1: {myHT1.ContainsKey("first")}");
        Console.WriteLine($"first is in myHT2: {myHT2.ContainsKey("first")}");
        Console.WriteLine($"first is in myHT3: {myHT3.ContainsKey("first")}");
    }
}


/*
This code produces the following output.
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

Imports System.Collections
Imports System.Globalization

Public Class myCultureComparer
    Implements IEqualityComparer

    Dim myComparer As CaseInsensitiveComparer

    Public Sub New()
        myComparer = CaseInsensitiveComparer.DefaultInvariant
    End Sub

    Public Sub New(ByVal myCulture As CultureInfo)
        myComparer = New CaseInsensitiveComparer(myCulture)
    End Sub

    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        Return myComparer.Compare(x, y) = 0
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode
        Return obj.ToString().ToLower().GetHashCode()
    End Function
End Class

Public Class SamplesHashtable   

   Public Shared Sub Main()

      ' Create the dictionary.
      Dim mySL As New SortedList()
      mySL.Add("FIRST", "Hello")
      mySL.Add("SECOND", "World")
      mySL.Add("THIRD", "!")

      ' Create a hash table using the default comparer.
      Dim myHT1 As New Hashtable(mySL)

      ' Create a hash table using the specified IEqualityComparer that uses
      ' the CaseInsensitiveComparer.DefaultInvariant to determine equality.
      Dim myHT2 As New Hashtable(mySL, New myCultureComparer())

      ' Create a hash table using an IEqualityComparer that is based on
      ' the Turkish culture (tr-TR) where "I" is not the uppercase
      ' version of "i".
      Dim myCul As New CultureInfo("tr-TR")
      Dim myHT3 As New Hashtable(mySL, New myCultureComparer(myCul))

      ' Search for a key in each hash table.
      Console.WriteLine($"first is in myHT1: {myHT1.ContainsKey("first")}")
      Console.WriteLine($"first is in myHT2: {myHT2.ContainsKey("first")}")
      Console.WriteLine($"first is in myHT3: {myHT3.ContainsKey("first")}")

   End Sub

End Class


'This code produces the following output.
'Results vary depending on the system's culture settings.
'
'first is in myHT1: False
'first is in myHT2: True
'first is in myHT3: False

Remarks

The initial capacity is set to the number of elements in the source dictionary. Capacity is automatically increased as required based on the load factor.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The hash code provider dispenses hash codes for keys in the Hashtable object. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

The custom hash code provider and the custom comparer enable scenarios such as doing lookups with case-insensitive strings.

The elements of the new Hashtable are sorted in the same order in which the enumerator iterates through the IDictionary object.

This constructor is an O(n) operation, where n is the number of elements in the d parameter.

See also

• IDictionary
• IHashCodeProvider
• IComparer
• GetHashCode()
• Equals(Object)

Hashtable(Int32, Single)

Source:

Hashtable.cs

Initializes a new, empty instance of the Hashtable class using the specified initial capacity and load factor, and the default hash code provider and comparer.

public:
 Hashtable(int capacity, float loadFactor);

public Hashtable (int capacity, float loadFactor);

new System.Collections.Hashtable : int * single -> System.Collections.Hashtable

Public Sub New (capacity As Integer, loadFactor As Single)

Parameters

capacity

Int32

The approximate number of elements that the Hashtable object can initially contain.

loadFactor

Single

A number in the range from 0.1 through 1.0 that is multiplied by the default value which provides the best performance. The result is the maximum ratio of elements to buckets.

Exceptions

ArgumentOutOfRangeException

capacity is less than zero.

-or-

loadFactor is less than 0.1.

-or-

loadFactor is greater than 1.0.

ArgumentException

capacity is causing an overflow.

Examples

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using namespace System;
using namespace System::Collections;
using namespace System::Globalization;

ref class myCultureComparer : public IEqualityComparer
{
public:
    CaseInsensitiveComparer^ myComparer;

public:
    myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer::DefaultInvariant;
    }

public:
    myCultureComparer(CultureInfo^ myCulture)
    {
        myComparer = gcnew CaseInsensitiveComparer(myCulture);
    }

public:
    virtual bool Equals(Object^ x, Object^ y)
    {
        if (myComparer->Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

public:
    virtual int GetHashCode(Object^ obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

public ref class SamplesHashtable
{

public:
    static void Main()
    {
        // Create a hash table using the default comparer.
        Hashtable^ myHT1 = gcnew Hashtable(3, .8f);
        myHT1->Add("FIRST", "Hello");
        myHT1->Add("SECOND", "World");
        myHT1->Add("THIRD", "!");

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable^ myHT2 = gcnew Hashtable(3, .8f, gcnew myCultureComparer());
        myHT2->Add("FIRST", "Hello");
        myHT2->Add("SECOND", "World");
        myHT2->Add("THIRD", "!");

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo^ myCul = gcnew CultureInfo("tr-TR");
        Hashtable^ myHT3 = gcnew Hashtable(3, .8f, gcnew myCultureComparer(myCul));
        myHT3->Add("FIRST", "Hello");
        myHT3->Add("SECOND", "World");
        myHT3->Add("THIRD", "!");

        // Search for a key in each hash table.
        Console::WriteLine("first is in myHT1: {0}", myHT1->ContainsKey("first"));
        Console::WriteLine("first is in myHT2: {0}", myHT2->ContainsKey("first"));
        Console::WriteLine("first is in myHT3: {0}", myHT3->ContainsKey("first"));

    }
};

int main()
{
    SamplesHashtable::Main();
}

/* 
This code produces the following output.  Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

using System;
using System.Collections;
using System.Globalization;

class myCultureComparer : IEqualityComparer
{
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public myCultureComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    public new bool Equals(object x, object y)
    {
        if (myComparer.Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public int GetHashCode(object obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj.ToString().ToLower().GetHashCode();
    }
}

public class SamplesHashtable
{

    public static void Main()
    {

        // Create a hash table using the default comparer.
        Hashtable myHT1 = new Hashtable(3, .8f);
        myHT1.Add("FIRST", "Hello");
        myHT1.Add("SECOND", "World");
        myHT1.Add("THIRD", "!");

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable myHT2 = new Hashtable(3, .8f, new myCultureComparer());
        myHT2.Add("FIRST", "Hello");
        myHT2.Add("SECOND", "World");
        myHT2.Add("THIRD", "!");

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo myCul = new CultureInfo("tr-TR");
        Hashtable myHT3 = new Hashtable(3, .8f, new myCultureComparer(myCul));

        myHT3.Add("FIRST", "Hello");
        myHT3.Add("SECOND", "World");
        myHT3.Add("THIRD", "!");

        // Search for a key in each hash table.
        Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"));
        Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"));
        Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"));
    }
}


/*
This code produces the following output.
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

Imports System.Collections
Imports System.Globalization

Public Class myCultureComparer
    Implements IEqualityComparer

    Dim myComparer As CaseInsensitiveComparer

    Public Sub New()
        myComparer = CaseInsensitiveComparer.DefaultInvariant
    End Sub

    Public Sub New(ByVal myCulture As CultureInfo)
        myComparer = New CaseInsensitiveComparer(myCulture)
    End Sub

    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        If (myComparer.Compare(x, y) = 0) Then
            Return True
        Else
            Return False
        End If
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode
        Return obj.ToString().ToLower().GetHashCode()
    End Function
End Class

Public Class SamplesHashtable

    Public Shared Sub Main()

        ' Create a hash table using the default comparer.
        Dim myHT1 As New Hashtable(3, System.Convert.ToSingle(0.8))
        myHT1.Add("FIRST", "Hello")
        myHT1.Add("SECOND", "World")
        myHT1.Add("THIRD", "!")

        ' Create a hash table using the specified IEqualityComparer that uses
        ' the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Dim myHT2 As New Hashtable(3, System.Convert.ToSingle(0.8), _
            New myCultureComparer())

        myHT2.Add("FIRST", "Hello")
        myHT2.Add("SECOND", "World")
        myHT2.Add("THIRD", "!")

        ' Create a hash table using an IEqualityComparer that is based on
        ' the Turkish culture (tr-TR) where "I" is not the uppercase
        ' version of "i".
        Dim myCul As New CultureInfo("tr-TR")
        Dim myHT3 As New Hashtable(3, System.Convert.ToSingle(0.8), _
            New myCultureComparer(myCul))

        myHT3.Add("FIRST", "Hello")
        myHT3.Add("SECOND", "World")
        myHT3.Add("THIRD", "!")

        ' Search for a key in each hash table.
        Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"))
        Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"))
        Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"))

    End Sub

End Class


'This code produces the following output.
'Results vary depending on the system's culture settings.
'
'first is in myHT1: False
'first is in myHT2: True
'first is in myHT3: False

Remarks

Specifying the initial capacity eliminates the need to perform a number of resizing operations while adding elements to the Hashtable object. Capacity is automatically increased as required based on the load factor.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption. A load factor of 1.0 is the best balance between speed and size.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The hash code provider dispenses hash codes for keys in the Hashtable. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

This constructor is an O(n) operation, where n is the capacity parameter.

See also

• GetHashCode()
• Equals(Object)

Hashtable(SerializationInfo, StreamingContext)

Source:

Hashtable.cs

Caution

This API supports obsolete formatter-based serialization. It should not be called or extended by application code.

Initializes a new, empty instance of the Hashtable class that is serializable using the specified SerializationInfo and StreamingContext objects.

protected:
 Hashtable(System::Runtime::Serialization::SerializationInfo ^ info, System::Runtime::Serialization::StreamingContext context);

[System.Obsolete("This API supports obsolete formatter-based serialization. It should not be called or extended by application code.", DiagnosticId="SYSLIB0051", UrlFormat="https://aka.ms/dotnet-warnings/{0}")]
protected Hashtable (System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context);

[<System.Obsolete("This API supports obsolete formatter-based serialization. It should not be called or extended by application code.", DiagnosticId="SYSLIB0051", UrlFormat="https://aka.ms/dotnet-warnings/{0}")>]
new System.Collections.Hashtable : System.Runtime.Serialization.SerializationInfo * System.Runtime.Serialization.StreamingContext -> System.Collections.Hashtable

Protected Sub New (info As SerializationInfo, context As StreamingContext)

Parameters

info

SerializationInfo

A SerializationInfo object containing the information required to serialize the Hashtable object.

context

StreamingContext

A StreamingContext object containing the source and destination of the serialized stream associated with the Hashtable.

Attributes

ObsoleteAttribute

Exceptions

ArgumentNullException

info is null.

Remarks

A hash table's capacity is used to calculate the optimal number of hash table buckets based on the load factor. Capacity is automatically increased as required.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The hash code provider dispenses hash codes for keys in the Hashtable object. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

This constructor is an O(n) operation, where n is Count.

Because serializing and deserializing an enumerator for a Hashtable can cause the elements to become reordered, it is not possible to continue enumeration without calling the Reset method.

See also

• ISerializable
• SerializationInfo
• StreamingContext
• OnDeserialization(Object)
• GetHashCode()
• Equals(Object)

Hashtable(IHashCodeProvider, IComparer)

Source:

Hashtable.cs

Caution

This constructor has been deprecated. Use Hashtable(IEqualityComparer) instead.

Initializes a new, empty instance of the Hashtable class using the default initial capacity and load factor, and the specified hash code provider and comparer.

public:
 Hashtable(System::Collections::IHashCodeProvider ^ hcp, System::Collections::IComparer ^ comparer);

[System.Obsolete("This constructor has been deprecated. Use Hashtable(IEqualityComparer) instead.")]
public Hashtable (System.Collections.IHashCodeProvider? hcp, System.Collections.IComparer? comparer);

[<System.Obsolete("This constructor has been deprecated. Use Hashtable(IEqualityComparer) instead.")>]
new System.Collections.Hashtable : System.Collections.IHashCodeProvider * System.Collections.IComparer -> System.Collections.Hashtable

Public Sub New (hcp As IHashCodeProvider, comparer As IComparer)

Parameters

hcp

IHashCodeProvider

The IHashCodeProvider object that supplies the hash codes for all keys in the Hashtable object.

-or-

null to use the default hash code provider, which is each key's implementation of GetHashCode().

comparer

IComparer

The IComparer object to use to determine whether two keys are equal.

-or-

null to use the default comparer, which is each key's implementation of Equals(Object).

Attributes

ObsoleteAttribute

Examples

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using namespace System;
using namespace System::Collections;
using namespace System::Globalization;

ref class myComparer : IEqualityComparer
{
public:
    virtual bool Equals(Object^ x, Object^ y) 
    {
        return x->Equals(y);
    }

    virtual int GetHashCode(Object^ obj)
    {
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

ref class myCultureComparer : IEqualityComparer
{
private:
    CaseInsensitiveComparer^ myComparer;

public:
    myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer::DefaultInvariant;
    }

    myCultureComparer(CultureInfo^ myCulture)
    {
        myComparer = gcnew CaseInsensitiveComparer(myCulture);
    }

    virtual bool Equals(Object^ x, Object^ y) 
    {
        if (myComparer->Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    virtual int GetHashCode(Object^ obj)
    {
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

int main()
{
   
   // Create a hash table using the default hash code provider and the default comparer.
   Hashtable^ myHT1 = gcnew Hashtable((IEqualityComparer^)nullptr);
   myHT1->Add( "FIRST", "Hello" );
   myHT1->Add( "SECOND", "World" );
   myHT1->Add( "THIRD", "!" );
   
   // Create a hash table using the specified IEqualityComparer that uses
   // the default Object.Equals to determine equality.
   Hashtable^ myHT2 = gcnew Hashtable(gcnew myComparer());
   myHT2->Add( "FIRST", "Hello" );
   myHT2->Add( "SECOND", "World" );
   myHT2->Add( "THIRD", "!" );
   
   // Create a hash table using a case-insensitive hash code provider and
   // case-insensitive comparer based on the InvariantCulture.
   Hashtable^ myHT3 = gcnew Hashtable(
            CaseInsensitiveHashCodeProvider::DefaultInvariant,
            CaseInsensitiveComparer::DefaultInvariant);
   myHT3->Add( "FIRST", "Hello" );
   myHT3->Add( "SECOND", "World" );
   myHT3->Add( "THIRD", "!" );
   
   // Create a hash table using an IEqualityComparer that is based on
   // the Turkish culture (tr-TR) where "I" is not the uppercase
   // version of "i".
   CultureInfo^ myCul = gcnew CultureInfo("tr-TR");
   Hashtable^ myHT4 = gcnew Hashtable( gcnew myCultureComparer(myCul) );
   myHT4->Add( "FIRST", "Hello" );
   myHT4->Add( "SECOND", "World" );
   myHT4->Add( "THIRD", "!" );
   
   // Search for a key in each hash table.
   Console::WriteLine( "first is in myHT1: {0}", myHT1->ContainsKey( "first" ) );
   Console::WriteLine( "first is in myHT2: {0}", myHT2->ContainsKey( "first" ) );
   Console::WriteLine( "first is in myHT3: {0}", myHT3->ContainsKey( "first" ) );
   Console::WriteLine( "first is in myHT4: {0}", myHT4->ContainsKey( "first" ) );
}

/* 
This code produces the following output.  Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: False
first is in myHT3: True
first is in myHT4: False

*/

using System;
using System.Collections;
using System.Globalization;

class myComparer : IEqualityComparer
{
    public new bool Equals(object x, object y)
    {
        return x.Equals(y);
    }

    public int GetHashCode(object obj)
    {
        return obj.ToString().ToLower().GetHashCode();
    }
}

class myCultureComparer : IEqualityComparer
{
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public myCultureComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    public new bool Equals(object x, object y)
    {
        return myComparer.Compare(x, y) == 0;
    }

    public int GetHashCode(object obj)
    {
        return obj.ToString().ToLower().GetHashCode();
    }
}

public class SamplesHashtable
{

    public static void Main()
    {

        // Create a hash table using the default comparer.
        var myHT1 = new Hashtable();
        myHT1.Add("FIRST", "Hello");
        myHT1.Add("SECOND", "World");
        myHT1.Add("THIRD", "!");

        // Create a hash table using the specified IEqualityComparer that uses
        // the default Object.Equals to determine equality.
        var myHT2 = new Hashtable(new myComparer());
        myHT2.Add("FIRST", "Hello");
        myHT2.Add("SECOND", "World");
        myHT2.Add("THIRD", "!");

        // Create a hash table using a case-insensitive hash code provider and
        // case-insensitive comparer based on the InvariantCulture.
        Hashtable myHT3 = new Hashtable(
            CaseInsensitiveHashCodeProvider.DefaultInvariant,
            CaseInsensitiveComparer.DefaultInvariant);
        myHT3.Add("FIRST", "Hello");
        myHT3.Add("SECOND", "World");
        myHT3.Add("THIRD", "!");

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        var myCul = new CultureInfo("tr-TR");
        var myHT4 = new Hashtable(new myCultureComparer(myCul));
        myHT4.Add("FIRST", "Hello");
        myHT4.Add("SECOND", "World");
        myHT4.Add("THIRD", "!");

        // Search for a key in each hash table.
        Console.WriteLine($"first is in myHT1: {myHT1.ContainsKey("first")}");
        Console.WriteLine($"first is in myHT2: {myHT2.ContainsKey("first")}");
        Console.WriteLine($"first is in myHT3: {myHT3.ContainsKey("first")}");
        Console.WriteLine($"first is in myHT4: {myHT4.ContainsKey("first")}");
    }
}


/*
This code produces the following output.
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: False
first is in myHT3: True
first is in myHT4: False

*/

Imports System.Collections
Imports System.Globalization

Public Class myComparer
    Implements IEqualityComparer
    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        Return x.Equals(y)
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode

        Return obj.ToString().ToLower().GetHashCode()
    End Function

End Class

Public Class myCultureComparer
    Implements IEqualityComparer

    Dim myComparer As CaseInsensitiveComparer

    Public Sub New()
        myComparer = CaseInsensitiveComparer.DefaultInvariant
    End Sub

    Public Sub New(ByVal myCulture As CultureInfo)
        myComparer = New CaseInsensitiveComparer(myCulture)
    End Sub

    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        Return myComparer.Compare(x, y) = 0
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode
        Return obj.ToString().ToLower().GetHashCode()
    End Function
End Class

Public Class SamplesHashtable

    Public Shared Sub Main()

        ' Create a hash table using the default comparer.
        Dim myHT1 As New Hashtable()
        myHT1.Add("FIRST", "Hello")
        myHT1.Add("SECOND", "World")
        myHT1.Add("THIRD", "!")

        ' Create a hash table using the specified IEqualityComparer that uses
        ' the default Object.Equals to determine equality.
        Dim myHT2 As New Hashtable(New myComparer())
        myHT2.Add("FIRST", "Hello")
        myHT2.Add("SECOND", "World")
        myHT2.Add("THIRD", "!")

        ' Create a hash table using a case-insensitive hash code provider and
        ' case-insensitive comparer based on the InvariantCulture.
        Dim myHT3 As New Hashtable( _
            CaseInsensitiveHashCodeProvider.DefaultInvariant, _
            CaseInsensitiveComparer.DefaultInvariant)
        myHT3.Add("FIRST", "Hello")
        myHT3.Add("SECOND", "World")
        myHT3.Add("THIRD", "!")

        ' Create a hash table using an IEqualityComparer that is based on
        ' the Turkish culture (tr-TR) where "I" is not the uppercase
        ' version of "i".
        Dim myCul As New CultureInfo("tr-TR")
        Dim myHT4 As New Hashtable(New myCultureComparer(myCul))
        myHT4.Add("FIRST", "Hello")
        myHT4.Add("SECOND", "World")
        myHT4.Add("THIRD", "!")

        ' Search for a key in each hash table.
        Console.WriteLine($"first is in myHT1: {myHT1.ContainsKey("first")}")
        Console.WriteLine($"first is in myHT2: {myHT2.ContainsKey("first")}")
        Console.WriteLine($"first is in myHT3: {myHT3.ContainsKey("first")}")
        Console.WriteLine($"first is in myHT4: {myHT4.ContainsKey("first")}")

    End Sub

End Class

'This code produces the following output.
'Results vary depending on the system's culture settings.

'first is in myHT1: False
'first is in myHT2: False
'first is in myHT3: True
'first is in myHT4: False

Remarks

A hash table's capacity is used to calculate the optimal number of hash table buckets based on the load factor. Capacity is automatically increased as required.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The hash code provider dispenses hash codes for keys in the Hashtable object. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

The custom hash code provider and the custom comparer enable scenarios such as doing lookups with case-insensitive strings.

This constructor is an O(1) operation.

See also

• IHashCodeProvider
• IComparer
• GetHashCode()
• Equals(Object)

Hashtable(IDictionary, Single)

Source:

Hashtable.cs

Initializes a new instance of the Hashtable class by copying the elements from the specified dictionary to the new Hashtable object. The new Hashtable object has an initial capacity equal to the number of elements copied, and uses the specified load factor, and the default hash code provider and comparer.

public:
 Hashtable(System::Collections::IDictionary ^ d, float loadFactor);

public Hashtable (System.Collections.IDictionary d, float loadFactor);

new System.Collections.Hashtable : System.Collections.IDictionary * single -> System.Collections.Hashtable

Public Sub New (d As IDictionary, loadFactor As Single)

Parameters

d

IDictionary

The IDictionary object to copy to a new Hashtable object.

loadFactor

Single

A number in the range from 0.1 through 1.0 that is multiplied by the default value which provides the best performance. The result is the maximum ratio of elements to buckets.

Exceptions

ArgumentNullException

d is null.

ArgumentOutOfRangeException

loadFactor is less than 0.1.

-or-

loadFactor is greater than 1.0.

Examples

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using namespace System;
using namespace System::Collections;
using namespace System::Globalization;

ref class myCultureComparer : public IEqualityComparer
{
public:
    CaseInsensitiveComparer^ myComparer;

public:
    myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer::DefaultInvariant;
    }

public:
    myCultureComparer(CultureInfo^ myCulture)
    {
        myComparer = gcnew CaseInsensitiveComparer(myCulture);
    }

public:
    virtual bool Equals(Object^ x, Object^ y)
    {
        if (myComparer->Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

public:
    virtual int GetHashCode(Object^ obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

public ref class SamplesHashtable
{

public:
    static void Main()
    {
       
       // Create the dictionary.
       SortedList^ mySL = gcnew SortedList;
       mySL->Add( "FIRST", "Hello" );
       mySL->Add( "SECOND", "World" );
       mySL->Add( "THIRD", "!" );
       
       // Create a hash table using the default hash code provider and the default comparer.
       Hashtable^ myHT1 = gcnew Hashtable( mySL, .8f );
       
       // Create a hash table using the specified case-insensitive hash code provider and case-insensitive comparer.
       Hashtable^ myHT2 = gcnew Hashtable( mySL, .8f, gcnew myCultureComparer() );
       
       // Create a hash table using the specified KeyComparer.
       // The KeyComparer uses a case-insensitive hash code provider and a case-insensitive comparer,
       // which are based on the Turkish culture (tr-TR), where "I" is not the uppercase version of "i".
       CultureInfo^ myCul = gcnew CultureInfo( "tr-TR" );
       Hashtable^ myHT3 = gcnew Hashtable( mySL, .8f, gcnew myCultureComparer( myCul ) );
       
       // Search for a key in each hash table.
       Console::WriteLine( "first is in myHT1: {0}", myHT1->ContainsKey( "first" ) );
       Console::WriteLine( "first is in myHT2: {0}", myHT2->ContainsKey( "first" ) );
       Console::WriteLine( "first is in myHT3: {0}", myHT3->ContainsKey( "first" ) );
    }
};

int main()
{
    SamplesHashtable::Main();
}

/* 
This code produces the following output.  Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

using System;
using System.Collections;
using System.Globalization;

class myCultureComparer : IEqualityComparer
{
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public myCultureComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    public new bool Equals(object x, object y)
    {
        if (myComparer.Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public int GetHashCode(object obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj.ToString().ToLower().GetHashCode();
    }
}

public class SamplesHashtable
{

    public static void Main()
    {

        // Create the dictionary.
        SortedList mySL = new SortedList();
        mySL.Add("FIRST", "Hello");
        mySL.Add("SECOND", "World");
        mySL.Add("THIRD", "!");

        // Create a hash table using the default comparer.
        Hashtable myHT1 = new Hashtable(mySL, .8f);

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable myHT2 = new Hashtable(mySL, .8f,
            new myCultureComparer());

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo myCul = new CultureInfo("tr-TR");
        Hashtable myHT3 = new Hashtable(mySL, .8f, new myCultureComparer(myCul));

        // Search for a key in each hash table.
        Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"));
        Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"));
        Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"));
    }
}


/*
This code produces the following output.
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

Imports System.Collections
Imports System.Globalization

Public Class myCultureComparer
    Implements IEqualityComparer

    Dim myComparer As CaseInsensitiveComparer

    Public Sub New()
        myComparer = CaseInsensitiveComparer.DefaultInvariant
    End Sub

    Public Sub New(ByVal myCulture As CultureInfo)
        myComparer = New CaseInsensitiveComparer(myCulture)
    End Sub

    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        If (myComparer.Compare(x, y) = 0) Then
            Return True
        Else
            Return False
        End If
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode
        Return obj.ToString().ToLower().GetHashCode()
    End Function
End Class

Public Class SamplesHashtable   

   Public Shared Sub Main()

      ' Create the dictionary.
      Dim mySL As New SortedList()
      mySL.Add("FIRST", "Hello")
      mySL.Add("SECOND", "World")
      mySL.Add("THIRD", "!")

      ' Create a hash table using the default comparer.
      Dim myHT1 As New Hashtable(mySL, System.Convert.ToSingle(0.8))

      ' Create a hash table using the specified IEqualityComparer that uses
      ' the CaseInsensitiveComparer.DefaultInvariant to determine equality.
      Dim myHT2 As New Hashtable(mySL, System.Convert.ToSingle(0.8), _
        New myCultureComparer())

      ' Create a hash table using an IEqualityComparer that is based on
      ' the Turkish culture (tr-TR) where "I" is not the uppercase
      ' version of "i".
      Dim myCul As New CultureInfo("tr-TR")
      Dim myHT3 As New Hashtable(mySL, System.Convert.ToSingle(0.8), _
        New myCultureComparer(myCul))

      ' Search for a key in each hash table.
      Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"))
      Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"))
      Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"))

   End Sub

End Class


'This code produces the following output.
'Results vary depending on the system's culture settings.
'
'first is in myHT1: False
'first is in myHT2: True
'first is in myHT3: False

Remarks

The initial capacity is set to the number of elements in the source dictionary. Capacity is automatically increased as required based on the load factor.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption. A load factor of 1.0 is the best balance between speed and size.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The hash code provider dispenses hash codes for keys in the Hashtable object. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

The elements of the new Hashtable are sorted in the same order in which the enumerator iterates through the IDictionary object.

This constructor is an O(n) operation, where n is the number of elements in the d parameter.

See also

• IDictionary
• GetHashCode()
• Equals(Object)

Hashtable(IDictionary, IEqualityComparer)

Source:

Hashtable.cs

Initializes a new instance of the Hashtable class by copying the elements from the specified dictionary to a new Hashtable object. The new Hashtable object has an initial capacity equal to the number of elements copied, and uses the default load factor and the specified IEqualityComparer object.

public:
 Hashtable(System::Collections::IDictionary ^ d, System::Collections::IEqualityComparer ^ equalityComparer);

public Hashtable (System.Collections.IDictionary d, System.Collections.IEqualityComparer? equalityComparer);

new System.Collections.Hashtable : System.Collections.IDictionary * System.Collections.IEqualityComparer -> System.Collections.Hashtable

Public Sub New (d As IDictionary, equalityComparer As IEqualityComparer)

Parameters

d

IDictionary

The IDictionary object to copy to a new Hashtable object.

equalityComparer

IEqualityComparer

The IEqualityComparer object that defines the hash code provider and the comparer to use with the Hashtable.

-or-

null to use the default hash code provider and the default comparer. The default hash code provider is each key's implementation of GetHashCode() and the default comparer is each key's implementation of Equals(Object).

Exceptions

ArgumentNullException

d is null.

Examples

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using namespace System;
using namespace System::Collections;
using namespace System::Globalization;

ref class myCultureComparer : public IEqualityComparer
{
public:
    CaseInsensitiveComparer^ myComparer;

public:
    myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer::DefaultInvariant;
    }

public:
    myCultureComparer(CultureInfo^ myCulture)
    {
        myComparer = gcnew CaseInsensitiveComparer(myCulture);
    }

public:
    virtual bool Equals(Object^ x, Object^ y)
    {
        if (myComparer->Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

public:
    virtual int GetHashCode(Object^ obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

public ref class SamplesHashtable
{

public:
    static void Main()
    {
        // Create the dictionary.
        SortedList^ mySL = gcnew SortedList();
        mySL->Add("FIRST", "Hello");
        mySL->Add("SECOND", "World");
        mySL->Add("THIRD", "!");

        // Create a hash table using the default comparer.
        Hashtable^ myHT1 = gcnew Hashtable(mySL);

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable^ myHT2 = gcnew Hashtable(mySL, gcnew myCultureComparer());

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo^ myCul = gcnew CultureInfo("tr-TR");
        Hashtable^ myHT3 = gcnew Hashtable(mySL, gcnew myCultureComparer(myCul));

        // Search for a key in each hash table.
        Console::WriteLine("first is in myHT1: {0}", myHT1->ContainsKey("first"));
        Console::WriteLine("first is in myHT2: {0}", myHT2->ContainsKey("first"));
        Console::WriteLine("first is in myHT3: {0}", myHT3->ContainsKey("first"));
    }
};

int main()
{
    SamplesHashtable::Main();
};

/* 
This code produces the following output. 
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

using System;
using System.Collections;
using System.Globalization;

class myCultureComparer : IEqualityComparer
{
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public myCultureComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    public new bool Equals(object x, object y)
    {
        return myComparer.Compare(x, y) == 0;
    }

    public int GetHashCode(object obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj.ToString().ToLower().GetHashCode();
    }
}

public class SamplesHashtable
{

    public static void Main()
    {

        // Create the dictionary.
        var mySL = new SortedList();
        mySL.Add("FIRST", "Hello");
        mySL.Add("SECOND", "World");
        mySL.Add("THIRD", "!");

        // Create a hash table using the default comparer.
        var myHT1 = new Hashtable(mySL);

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        var myHT2 = new Hashtable(mySL, new myCultureComparer());

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        var myCul = new CultureInfo("tr-TR");
        var myHT3 = new Hashtable(mySL, new myCultureComparer(myCul));

        // Search for a key in each hash table.
        Console.WriteLine($"first is in myHT1: {myHT1.ContainsKey("first")}");
        Console.WriteLine($"first is in myHT2: {myHT2.ContainsKey("first")}");
        Console.WriteLine($"first is in myHT3: {myHT3.ContainsKey("first")}");
    }
}


/*
This code produces the following output.
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

Imports System.Collections
Imports System.Globalization

Public Class myCultureComparer
    Implements IEqualityComparer

    Dim myComparer As CaseInsensitiveComparer

    Public Sub New()
        myComparer = CaseInsensitiveComparer.DefaultInvariant
    End Sub

    Public Sub New(ByVal myCulture As CultureInfo)
        myComparer = New CaseInsensitiveComparer(myCulture)
    End Sub

    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        Return myComparer.Compare(x, y) = 0
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode
        Return obj.ToString().ToLower().GetHashCode()
    End Function
End Class

Public Class SamplesHashtable   

   Public Shared Sub Main()

      ' Create the dictionary.
      Dim mySL As New SortedList()
      mySL.Add("FIRST", "Hello")
      mySL.Add("SECOND", "World")
      mySL.Add("THIRD", "!")

      ' Create a hash table using the default comparer.
      Dim myHT1 As New Hashtable(mySL)

      ' Create a hash table using the specified IEqualityComparer that uses
      ' the CaseInsensitiveComparer.DefaultInvariant to determine equality.
      Dim myHT2 As New Hashtable(mySL, New myCultureComparer())

      ' Create a hash table using an IEqualityComparer that is based on
      ' the Turkish culture (tr-TR) where "I" is not the uppercase
      ' version of "i".
      Dim myCul As New CultureInfo("tr-TR")
      Dim myHT3 As New Hashtable(mySL, New myCultureComparer(myCul))

      ' Search for a key in each hash table.
      Console.WriteLine($"first is in myHT1: {myHT1.ContainsKey("first")}")
      Console.WriteLine($"first is in myHT2: {myHT2.ContainsKey("first")}")
      Console.WriteLine($"first is in myHT3: {myHT3.ContainsKey("first")}")

   End Sub

End Class


'This code produces the following output.
'Results vary depending on the system's culture settings.
'
'first is in myHT1: False
'first is in myHT2: True
'first is in myHT3: False

Remarks

The initial capacity is set to the number of elements in the source dictionary. Capacity is automatically increased as required based on the load factor.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The IEqualityComparer object includes both the hash code provider and the comparer. If an IEqualityComparer is used in the Hashtable constructor, the objects used as keys in the Hashtable object are not required to override the Object.GetHashCode and Object.Equals methods.

The hash code provider dispenses hash codes for keys in the Hashtable. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

The IEqualityComparer enables scenarios such as doing lookups with case-insensitive strings.

The elements of the new Hashtable are sorted in the same order in which the enumerator iterates through the IDictionary object.

This constructor is an O(n) operation, where n is the number of elements in the d parameter.

See also

• IDictionary
• IEqualityComparer

Hashtable(Int32)

Source:

Hashtable.cs

Initializes a new, empty instance of the Hashtable class using the specified initial capacity, and the default load factor, hash code provider, and comparer.

public:
 Hashtable(int capacity);

public Hashtable (int capacity);

new System.Collections.Hashtable : int -> System.Collections.Hashtable

Public Sub New (capacity As Integer)

Parameters

capacity

Int32

The approximate number of elements that the Hashtable object can initially contain.

Exceptions

ArgumentOutOfRangeException

capacity is less than zero.

Examples

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using namespace System;
using namespace System::Collections;
using namespace System::Globalization;

ref class myCultureComparer : public IEqualityComparer
{
public:
    CaseInsensitiveComparer^ myComparer;

public:
    myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer::DefaultInvariant;
    }

public:
    myCultureComparer(CultureInfo^ myCulture)
    {
        myComparer = gcnew CaseInsensitiveComparer(myCulture);
    }

public:
    virtual bool Equals(Object^ x, Object^ y)
    {
        if (myComparer->Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

public:
    virtual int GetHashCode(Object^ obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

public ref class SamplesHashtable
{

public:
    static void Main()
    {
        // Create a hash table using the default comparer.
        Hashtable^ myHT1 = gcnew Hashtable(3);
        myHT1->Add("FIRST", "Hello");
        myHT1->Add("SECOND", "World");
        myHT1->Add("THIRD", "!");

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable^ myHT2 = gcnew Hashtable(3, gcnew myCultureComparer());
        myHT2->Add("FIRST", "Hello");
        myHT2->Add("SECOND", "World");
        myHT2->Add("THIRD", "!");

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo^ myCul = gcnew CultureInfo("tr-TR");
        Hashtable^ myHT3 = gcnew Hashtable(3, gcnew myCultureComparer(myCul));
        myHT3->Add("FIRST", "Hello");
        myHT3->Add("SECOND", "World");
        myHT3->Add("THIRD", "!");

        // Search for a key in each hash table.
        Console::WriteLine("first is in myHT1: {0}", myHT1->ContainsKey("first"));
        Console::WriteLine("first is in myHT2: {0}", myHT2->ContainsKey("first"));
        Console::WriteLine("first is in myHT3: {0}", myHT3->ContainsKey("first"));

    }
};

int main()
{
    SamplesHashtable::Main();
}

/* 
This code produces the following output.  Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

using System;
using System.Collections;
using System.Globalization;

class myCultureComparer : IEqualityComparer
{
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public myCultureComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    public new bool Equals(object x, object y)
    {
        if (myComparer.Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public int GetHashCode(object obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj.ToString().ToLower().GetHashCode();
    }
}

public class SamplesHashtable
{

    public static void Main()
    {

        // Create a hash table using the default comparer.
        Hashtable myHT1 = new Hashtable(3);
        myHT1.Add("FIRST", "Hello");
        myHT1.Add("SECOND", "World");
        myHT1.Add("THIRD", "!");

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable myHT2 = new Hashtable(3, new myCultureComparer());
        myHT2.Add("FIRST", "Hello");
        myHT2.Add("SECOND", "World");
        myHT2.Add("THIRD", "!");

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo myCul = new CultureInfo("tr-TR");
        Hashtable myHT3 = new Hashtable(3, new myCultureComparer(myCul));
        myHT3.Add("FIRST", "Hello");
        myHT3.Add("SECOND", "World");
        myHT3.Add("THIRD", "!");

        // Search for a key in each hash table.
        Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"));
        Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"));
        Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"));
    }
}


/*
This code produces the following output.
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

Imports System.Collections
Imports System.Globalization

Public Class myCultureComparer
    Implements IEqualityComparer

    Dim myComparer As CaseInsensitiveComparer

    Public Sub New()
        myComparer = CaseInsensitiveComparer.DefaultInvariant
    End Sub

    Public Sub New(ByVal myCulture As CultureInfo)
        myComparer = New CaseInsensitiveComparer(myCulture)
    End Sub

    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        If (myComparer.Compare(x, y) = 0) Then
            Return True
        Else
            Return False
        End If
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode
        Return obj.ToString().ToLower().GetHashCode()
    End Function
End Class

Public Class SamplesHashtable   

   Public Shared Sub Main()

      ' Create a hash table using the default comparer.
      Dim myHT1 As New Hashtable(3)
      myHT1.Add("FIRST", "Hello")
      myHT1.Add("SECOND", "World")
      myHT1.Add("THIRD", "!")

      ' Create a hash table using the specified IEqualityComparer that uses
      ' the CaseInsensitiveComparer.DefaultInvariant to determine equality.
      Dim myHT2 As New Hashtable(3, New myCultureComparer())
      myHT2.Add("FIRST", "Hello")
      myHT2.Add("SECOND", "World")
      myHT2.Add("THIRD", "!")

      ' Create a hash table using an IEqualityComparer that is based on
      ' the Turkish culture (tr-TR) where "I" is not the uppercase
      ' version of "i".
      Dim myCul As New CultureInfo("tr-TR")
      Dim myHT3 As New Hashtable(3, New myCultureComparer(myCul))
      myHT3.Add("FIRST", "Hello")
      myHT3.Add("SECOND", "World")
      myHT3.Add("THIRD", "!")

      ' Search for a key in each hash table.
      Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"))
      Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"))
      Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"))

   End Sub

End Class


'This code produces the following output.
'Results vary depending on the system's culture settings.
'
'first is in myHT1: False
'first is in myHT2: True
'first is in myHT3: False

Remarks

Specifying the initial capacity eliminates the need to perform a number of resizing operations while adding elements to the Hashtable object. Capacity is automatically increased as required based on the load factor.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The hash code provider dispenses hash codes for keys in the Hashtable. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

This constructor is an O(n) operation, where n is capacity.

See also

• GetHashCode()
• Equals(Object)

Hashtable(IEqualityComparer)

Source:

Hashtable.cs

Initializes a new, empty instance of the Hashtable class using the default initial capacity and load factor, and the specified IEqualityComparer object.

public:
 Hashtable(System::Collections::IEqualityComparer ^ equalityComparer);

public Hashtable (System.Collections.IEqualityComparer? equalityComparer);

new System.Collections.Hashtable : System.Collections.IEqualityComparer -> System.Collections.Hashtable

Public Sub New (equalityComparer As IEqualityComparer)

Parameters

equalityComparer

IEqualityComparer

The IEqualityComparer object that defines the hash code provider and the comparer to use with the Hashtable object.

-or-

null to use the default hash code provider and the default comparer. The default hash code provider is each key's implementation of GetHashCode() and the default comparer is each key's implementation of Equals(Object).

Examples

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using namespace System;
using namespace System::Collections;
using namespace System::Globalization;

ref class myComparer : IEqualityComparer
{
public:
    virtual bool Equals(Object^ x, Object^ y) 
    {
        return x->Equals(y);
    }

    virtual int GetHashCode(Object^ obj)
    {
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

ref class myCultureComparer : IEqualityComparer
{
private:
    CaseInsensitiveComparer^ myComparer;

public:
    myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer::DefaultInvariant;
    }

    myCultureComparer(CultureInfo^ myCulture)
    {
        myComparer = gcnew CaseInsensitiveComparer(myCulture);
    }

    virtual bool Equals(Object^ x, Object^ y) 
    {
        if (myComparer->Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    virtual int GetHashCode(Object^ obj)
    {
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

int main()
{
   
   // Create a hash table using the default hash code provider and the default comparer.
   Hashtable^ myHT1 = gcnew Hashtable((IEqualityComparer^)nullptr);
   myHT1->Add( "FIRST", "Hello" );
   myHT1->Add( "SECOND", "World" );
   myHT1->Add( "THIRD", "!" );
   
   // Create a hash table using the specified IEqualityComparer that uses
   // the default Object.Equals to determine equality.
   Hashtable^ myHT2 = gcnew Hashtable(gcnew myComparer());
   myHT2->Add( "FIRST", "Hello" );
   myHT2->Add( "SECOND", "World" );
   myHT2->Add( "THIRD", "!" );
   
   // Create a hash table using a case-insensitive hash code provider and
   // case-insensitive comparer based on the InvariantCulture.
   Hashtable^ myHT3 = gcnew Hashtable(
            CaseInsensitiveHashCodeProvider::DefaultInvariant,
            CaseInsensitiveComparer::DefaultInvariant);
   myHT3->Add( "FIRST", "Hello" );
   myHT3->Add( "SECOND", "World" );
   myHT3->Add( "THIRD", "!" );
   
   // Create a hash table using an IEqualityComparer that is based on
   // the Turkish culture (tr-TR) where "I" is not the uppercase
   // version of "i".
   CultureInfo^ myCul = gcnew CultureInfo("tr-TR");
   Hashtable^ myHT4 = gcnew Hashtable( gcnew myCultureComparer(myCul) );
   myHT4->Add( "FIRST", "Hello" );
   myHT4->Add( "SECOND", "World" );
   myHT4->Add( "THIRD", "!" );
   
   // Search for a key in each hash table.
   Console::WriteLine( "first is in myHT1: {0}", myHT1->ContainsKey( "first" ) );
   Console::WriteLine( "first is in myHT2: {0}", myHT2->ContainsKey( "first" ) );
   Console::WriteLine( "first is in myHT3: {0}", myHT3->ContainsKey( "first" ) );
   Console::WriteLine( "first is in myHT4: {0}", myHT4->ContainsKey( "first" ) );
}

/* 
This code produces the following output.  Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: False
first is in myHT3: True
first is in myHT4: False

*/

using System;
using System.Collections;
using System.Globalization;

class myComparer : IEqualityComparer
{
    public new bool Equals(object x, object y)
    {
        return x.Equals(y);
    }

    public int GetHashCode(object obj)
    {
        return obj.ToString().ToLower().GetHashCode();
    }
}

class myCultureComparer : IEqualityComparer
{
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public myCultureComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    public new bool Equals(object x, object y)
    {
        return myComparer.Compare(x, y) == 0;
    }

    public int GetHashCode(object obj)
    {
        return obj.ToString().ToLower().GetHashCode();
    }
}

public class SamplesHashtable
{

    public static void Main()
    {

        // Create a hash table using the default comparer.
        var myHT1 = new Hashtable();
        myHT1.Add("FIRST", "Hello");
        myHT1.Add("SECOND", "World");
        myHT1.Add("THIRD", "!");

        // Create a hash table using the specified IEqualityComparer that uses
        // the default Object.Equals to determine equality.
        var myHT2 = new Hashtable(new myComparer());
        myHT2.Add("FIRST", "Hello");
        myHT2.Add("SECOND", "World");
        myHT2.Add("THIRD", "!");

        // Create a hash table using a case-insensitive hash code provider and
        // case-insensitive comparer based on the InvariantCulture.
        Hashtable myHT3 = new Hashtable(
            CaseInsensitiveHashCodeProvider.DefaultInvariant,
            CaseInsensitiveComparer.DefaultInvariant);
        myHT3.Add("FIRST", "Hello");
        myHT3.Add("SECOND", "World");
        myHT3.Add("THIRD", "!");

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        var myCul = new CultureInfo("tr-TR");
        var myHT4 = new Hashtable(new myCultureComparer(myCul));
        myHT4.Add("FIRST", "Hello");
        myHT4.Add("SECOND", "World");
        myHT4.Add("THIRD", "!");

        // Search for a key in each hash table.
        Console.WriteLine($"first is in myHT1: {myHT1.ContainsKey("first")}");
        Console.WriteLine($"first is in myHT2: {myHT2.ContainsKey("first")}");
        Console.WriteLine($"first is in myHT3: {myHT3.ContainsKey("first")}");
        Console.WriteLine($"first is in myHT4: {myHT4.ContainsKey("first")}");
    }
}


/*
This code produces the following output.
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: False
first is in myHT3: True
first is in myHT4: False

*/

Imports System.Collections
Imports System.Globalization

Public Class myComparer
    Implements IEqualityComparer
    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        Return x.Equals(y)
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode

        Return obj.ToString().ToLower().GetHashCode()
    End Function

End Class

Public Class myCultureComparer
    Implements IEqualityComparer

    Dim myComparer As CaseInsensitiveComparer

    Public Sub New()
        myComparer = CaseInsensitiveComparer.DefaultInvariant
    End Sub

    Public Sub New(ByVal myCulture As CultureInfo)
        myComparer = New CaseInsensitiveComparer(myCulture)
    End Sub

    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        Return myComparer.Compare(x, y) = 0
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode
        Return obj.ToString().ToLower().GetHashCode()
    End Function
End Class

Public Class SamplesHashtable

    Public Shared Sub Main()

        ' Create a hash table using the default comparer.
        Dim myHT1 As New Hashtable()
        myHT1.Add("FIRST", "Hello")
        myHT1.Add("SECOND", "World")
        myHT1.Add("THIRD", "!")

        ' Create a hash table using the specified IEqualityComparer that uses
        ' the default Object.Equals to determine equality.
        Dim myHT2 As New Hashtable(New myComparer())
        myHT2.Add("FIRST", "Hello")
        myHT2.Add("SECOND", "World")
        myHT2.Add("THIRD", "!")

        ' Create a hash table using a case-insensitive hash code provider and
        ' case-insensitive comparer based on the InvariantCulture.
        Dim myHT3 As New Hashtable( _
            CaseInsensitiveHashCodeProvider.DefaultInvariant, _
            CaseInsensitiveComparer.DefaultInvariant)
        myHT3.Add("FIRST", "Hello")
        myHT3.Add("SECOND", "World")
        myHT3.Add("THIRD", "!")

        ' Create a hash table using an IEqualityComparer that is based on
        ' the Turkish culture (tr-TR) where "I" is not the uppercase
        ' version of "i".
        Dim myCul As New CultureInfo("tr-TR")
        Dim myHT4 As New Hashtable(New myCultureComparer(myCul))
        myHT4.Add("FIRST", "Hello")
        myHT4.Add("SECOND", "World")
        myHT4.Add("THIRD", "!")

        ' Search for a key in each hash table.
        Console.WriteLine($"first is in myHT1: {myHT1.ContainsKey("first")}")
        Console.WriteLine($"first is in myHT2: {myHT2.ContainsKey("first")}")
        Console.WriteLine($"first is in myHT3: {myHT3.ContainsKey("first")}")
        Console.WriteLine($"first is in myHT4: {myHT4.ContainsKey("first")}")

    End Sub

End Class

'This code produces the following output.
'Results vary depending on the system's culture settings.

'first is in myHT1: False
'first is in myHT2: False
'first is in myHT3: True
'first is in myHT4: False

Remarks

A hash table's capacity is used to calculate the optimal number of hash table buckets based on the load factor. Capacity is automatically increased as required.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The IEqualityComparer object includes both the hash code provider and the comparer. If an IEqualityComparer is used in the Hashtable constructor, the objects used as keys in the Hashtable object are not required to override the Object.GetHashCode and Object.Equals methods.

The hash code provider dispenses hash codes for keys in the Hashtable. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

The IEqualityComparer enables scenarios such as doing lookups with case-insensitive strings.

This constructor is an O(1) operation.

See also

• IEqualityComparer

Hashtable(IDictionary)

Source:

Hashtable.cs

Initializes a new instance of the Hashtable class by copying the elements from the specified dictionary to the new Hashtable object. The new Hashtable object has an initial capacity equal to the number of elements copied, and uses the default load factor, hash code provider, and comparer.

public:
 Hashtable(System::Collections::IDictionary ^ d);

public Hashtable (System.Collections.IDictionary d);

new System.Collections.Hashtable : System.Collections.IDictionary -> System.Collections.Hashtable

Public Sub New (d As IDictionary)

Parameters

d

IDictionary

The IDictionary object to copy to a new Hashtable object.

Exceptions

ArgumentNullException

d is null.

Examples

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using namespace System;
using namespace System::Collections;
using namespace System::Globalization;

ref class myCultureComparer : public IEqualityComparer
{
public:
    CaseInsensitiveComparer^ myComparer;

public:
    myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer::DefaultInvariant;
    }

public:
    myCultureComparer(CultureInfo^ myCulture)
    {
        myComparer = gcnew CaseInsensitiveComparer(myCulture);
    }

public:
    virtual bool Equals(Object^ x, Object^ y)
    {
        if (myComparer->Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

public:
    virtual int GetHashCode(Object^ obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

public ref class SamplesHashtable
{

public:
    static void Main()
    {
        // Create the dictionary.
        SortedList^ mySL = gcnew SortedList();
        mySL->Add("FIRST", "Hello");
        mySL->Add("SECOND", "World");
        mySL->Add("THIRD", "!");

        // Create a hash table using the default comparer.
        Hashtable^ myHT1 = gcnew Hashtable(mySL);

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable^ myHT2 = gcnew Hashtable(mySL, gcnew myCultureComparer());

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo^ myCul = gcnew CultureInfo("tr-TR");
        Hashtable^ myHT3 = gcnew Hashtable(mySL, gcnew myCultureComparer(myCul));

        // Search for a key in each hash table.
        Console::WriteLine("first is in myHT1: {0}", myHT1->ContainsKey("first"));
        Console::WriteLine("first is in myHT2: {0}", myHT2->ContainsKey("first"));
        Console::WriteLine("first is in myHT3: {0}", myHT3->ContainsKey("first"));
    }
};

int main()
{
    SamplesHashtable::Main();
};

/* 
This code produces the following output. 
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

using System;
using System.Collections;
using System.Globalization;

class myCultureComparer : IEqualityComparer
{
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public myCultureComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    public new bool Equals(object x, object y)
    {
        return myComparer.Compare(x, y) == 0;
    }

    public int GetHashCode(object obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj.ToString().ToLower().GetHashCode();
    }
}

public class SamplesHashtable
{

    public static void Main()
    {

        // Create the dictionary.
        var mySL = new SortedList();
        mySL.Add("FIRST", "Hello");
        mySL.Add("SECOND", "World");
        mySL.Add("THIRD", "!");

        // Create a hash table using the default comparer.
        var myHT1 = new Hashtable(mySL);

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        var myHT2 = new Hashtable(mySL, new myCultureComparer());

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        var myCul = new CultureInfo("tr-TR");
        var myHT3 = new Hashtable(mySL, new myCultureComparer(myCul));

        // Search for a key in each hash table.
        Console.WriteLine($"first is in myHT1: {myHT1.ContainsKey("first")}");
        Console.WriteLine($"first is in myHT2: {myHT2.ContainsKey("first")}");
        Console.WriteLine($"first is in myHT3: {myHT3.ContainsKey("first")}");
    }
}


/*
This code produces the following output.
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

Imports System.Collections
Imports System.Globalization

Public Class myCultureComparer
    Implements IEqualityComparer

    Dim myComparer As CaseInsensitiveComparer

    Public Sub New()
        myComparer = CaseInsensitiveComparer.DefaultInvariant
    End Sub

    Public Sub New(ByVal myCulture As CultureInfo)
        myComparer = New CaseInsensitiveComparer(myCulture)
    End Sub

    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        Return myComparer.Compare(x, y) = 0
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode
        Return obj.ToString().ToLower().GetHashCode()
    End Function
End Class

Public Class SamplesHashtable   

   Public Shared Sub Main()

      ' Create the dictionary.
      Dim mySL As New SortedList()
      mySL.Add("FIRST", "Hello")
      mySL.Add("SECOND", "World")
      mySL.Add("THIRD", "!")

      ' Create a hash table using the default comparer.
      Dim myHT1 As New Hashtable(mySL)

      ' Create a hash table using the specified IEqualityComparer that uses
      ' the CaseInsensitiveComparer.DefaultInvariant to determine equality.
      Dim myHT2 As New Hashtable(mySL, New myCultureComparer())

      ' Create a hash table using an IEqualityComparer that is based on
      ' the Turkish culture (tr-TR) where "I" is not the uppercase
      ' version of "i".
      Dim myCul As New CultureInfo("tr-TR")
      Dim myHT3 As New Hashtable(mySL, New myCultureComparer(myCul))

      ' Search for a key in each hash table.
      Console.WriteLine($"first is in myHT1: {myHT1.ContainsKey("first")}")
      Console.WriteLine($"first is in myHT2: {myHT2.ContainsKey("first")}")
      Console.WriteLine($"first is in myHT3: {myHT3.ContainsKey("first")}")

   End Sub

End Class


'This code produces the following output.
'Results vary depending on the system's culture settings.
'
'first is in myHT1: False
'first is in myHT2: True
'first is in myHT3: False

Remarks

The initial capacity is set to the number of elements in the source dictionary. Capacity is automatically increased as required based on the load factor.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The hash code provider dispenses hash codes for keys in the Hashtable object. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

The elements of the new Hashtable are sorted in the same order in which the enumerator iterates through the IDictionary object.

This constructor is an O(n) operation, where n is the number of elements in the d parameter.

See also

• IDictionary
• GetHashCode()
• Equals(Object)

Hashtable(Int32, IEqualityComparer)

Source:

Hashtable.cs

Initializes a new, empty instance of the Hashtable class using the specified initial capacity and IEqualityComparer, and the default load factor.

public:
 Hashtable(int capacity, System::Collections::IEqualityComparer ^ equalityComparer);

public Hashtable (int capacity, System.Collections.IEqualityComparer? equalityComparer);

new System.Collections.Hashtable : int * System.Collections.IEqualityComparer -> System.Collections.Hashtable

Public Sub New (capacity As Integer, equalityComparer As IEqualityComparer)

Parameters

capacity

Int32

The approximate number of elements that the Hashtable object can initially contain.

equalityComparer

IEqualityComparer

The IEqualityComparer object that defines the hash code provider and the comparer to use with the Hashtable.

-or-

null to use the default hash code provider and the default comparer. The default hash code provider is each key's implementation of GetHashCode() and the default comparer is each key's implementation of Equals(Object).

Exceptions

ArgumentOutOfRangeException

capacity is less than zero.

Examples

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using namespace System;
using namespace System::Collections;
using namespace System::Globalization;

ref class myCultureComparer : public IEqualityComparer
{
public:
    CaseInsensitiveComparer^ myComparer;

public:
    myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer::DefaultInvariant;
    }

public:
    myCultureComparer(CultureInfo^ myCulture)
    {
        myComparer = gcnew CaseInsensitiveComparer(myCulture);
    }

public:
    virtual bool Equals(Object^ x, Object^ y)
    {
        if (myComparer->Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

public:
    virtual int GetHashCode(Object^ obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj->ToString()->ToLower()->GetHashCode();
    }
};

public ref class SamplesHashtable
{

public:
    static void Main()
    {
        // Create a hash table using the default comparer.
        Hashtable^ myHT1 = gcnew Hashtable(3);
        myHT1->Add("FIRST", "Hello");
        myHT1->Add("SECOND", "World");
        myHT1->Add("THIRD", "!");

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable^ myHT2 = gcnew Hashtable(3, gcnew myCultureComparer());
        myHT2->Add("FIRST", "Hello");
        myHT2->Add("SECOND", "World");
        myHT2->Add("THIRD", "!");

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo^ myCul = gcnew CultureInfo("tr-TR");
        Hashtable^ myHT3 = gcnew Hashtable(3, gcnew myCultureComparer(myCul));
        myHT3->Add("FIRST", "Hello");
        myHT3->Add("SECOND", "World");
        myHT3->Add("THIRD", "!");

        // Search for a key in each hash table.
        Console::WriteLine("first is in myHT1: {0}", myHT1->ContainsKey("first"));
        Console::WriteLine("first is in myHT2: {0}", myHT2->ContainsKey("first"));
        Console::WriteLine("first is in myHT3: {0}", myHT3->ContainsKey("first"));

    }
};

int main()
{
    SamplesHashtable::Main();
}

/* 
This code produces the following output.  Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

using System;
using System.Collections;
using System.Globalization;

class myCultureComparer : IEqualityComparer
{
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
    {
        myComparer = CaseInsensitiveComparer.DefaultInvariant;
    }

    public myCultureComparer(CultureInfo myCulture)
    {
        myComparer = new CaseInsensitiveComparer(myCulture);
    }

    public new bool Equals(object x, object y)
    {
        if (myComparer.Compare(x, y) == 0)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public int GetHashCode(object obj)
    {
        // Compare the hash code for the lowercase versions of the strings.
        return obj.ToString().ToLower().GetHashCode();
    }
}

public class SamplesHashtable
{

    public static void Main()
    {

        // Create a hash table using the default comparer.
        Hashtable myHT1 = new Hashtable(3);
        myHT1.Add("FIRST", "Hello");
        myHT1.Add("SECOND", "World");
        myHT1.Add("THIRD", "!");

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable myHT2 = new Hashtable(3, new myCultureComparer());
        myHT2.Add("FIRST", "Hello");
        myHT2.Add("SECOND", "World");
        myHT2.Add("THIRD", "!");

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo myCul = new CultureInfo("tr-TR");
        Hashtable myHT3 = new Hashtable(3, new myCultureComparer(myCul));
        myHT3.Add("FIRST", "Hello");
        myHT3.Add("SECOND", "World");
        myHT3.Add("THIRD", "!");

        // Search for a key in each hash table.
        Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"));
        Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"));
        Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"));
    }
}


/*
This code produces the following output.
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False

*/

Imports System.Collections
Imports System.Globalization

Public Class myCultureComparer
    Implements IEqualityComparer

    Dim myComparer As CaseInsensitiveComparer

    Public Sub New()
        myComparer = CaseInsensitiveComparer.DefaultInvariant
    End Sub

    Public Sub New(ByVal myCulture As CultureInfo)
        myComparer = New CaseInsensitiveComparer(myCulture)
    End Sub

    Public Function Equals1(ByVal x As Object, ByVal y As Object) _
        As Boolean Implements IEqualityComparer.Equals

        If (myComparer.Compare(x, y) = 0) Then
            Return True
        Else
            Return False
        End If
    End Function

    Public Function GetHashCode1(ByVal obj As Object) _
        As Integer Implements IEqualityComparer.GetHashCode
        Return obj.ToString().ToLower().GetHashCode()
    End Function
End Class

Public Class SamplesHashtable   

   Public Shared Sub Main()

      ' Create a hash table using the default comparer.
      Dim myHT1 As New Hashtable(3)
      myHT1.Add("FIRST", "Hello")
      myHT1.Add("SECOND", "World")
      myHT1.Add("THIRD", "!")

      ' Create a hash table using the specified IEqualityComparer that uses
      ' the CaseInsensitiveComparer.DefaultInvariant to determine equality.
      Dim myHT2 As New Hashtable(3, New myCultureComparer())
      myHT2.Add("FIRST", "Hello")
      myHT2.Add("SECOND", "World")
      myHT2.Add("THIRD", "!")

      ' Create a hash table using an IEqualityComparer that is based on
      ' the Turkish culture (tr-TR) where "I" is not the uppercase
      ' version of "i".
      Dim myCul As New CultureInfo("tr-TR")
      Dim myHT3 As New Hashtable(3, New myCultureComparer(myCul))
      myHT3.Add("FIRST", "Hello")
      myHT3.Add("SECOND", "World")
      myHT3.Add("THIRD", "!")

      ' Search for a key in each hash table.
      Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"))
      Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"))
      Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"))

   End Sub

End Class


'This code produces the following output.
'Results vary depending on the system's culture settings.
'
'first is in myHT1: False
'first is in myHT2: True
'first is in myHT3: False

Remarks

Specifying the initial capacity eliminates the need to perform a number of resizing operations while adding elements to the Hashtable object. Capacity is automatically increased as required based on the load factor.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The IEqualityComparer object includes both the hash code provider and the comparer. If an IEqualityComparer is used in the Hashtable constructor, the objects used as keys in the Hashtable are not required to override the Object.GetHashCode and Object.Equals methods.

The hash code provider dispenses hash codes for keys in the Hashtable. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

The IEqualityComparer enables scenarios such as doing lookups with case-insensitive strings.

This constructor is an O(n) operation, where n is the capacity parameter.

See also

• IEqualityComparer