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11/18/2011

Object Class

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Supports all classes in the .NET Framework class hierarchy and provides low-level services to derived classes. This is the ultimate base class of all classes in the .NET Framework; it is the root of the type hierarchy.

Inheritance Hierarchy

System.Object
All classes, structures, enumerations, and delegates.

Namespace: System
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
<ComVisibleAttribute(True)> _
<ClassInterfaceAttribute(ClassInterfaceType.AutoDual)> _
Public Class Object

[ComVisibleAttribute(true)]
[ClassInterfaceAttribute(ClassInterfaceType.AutoDual)]
public class Object

The Object type exposes the following members.

Constructors

	Name	Description
	Object	Initializes a new instance of the Object class.

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Methods

	Name	Description
	Equals(Object)	Determines whether the specified Object is equal to the current Object.
	Equals(Object, Object)	Determines whether the specified Object instances are considered equal.
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection.
	GetHashCode	Serves as a hash function for a particular type.
	GetType	Gets the Type of the current instance.
	MemberwiseClone	Creates a shallow copy of the current Object.
	ReferenceEquals	Determines whether the specified object instances are the same instance.
	ToString	Returns a string that represents the current object.

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Remarks

Languages typically do not require a class to declare inheritance from Object because the inheritance is implicit.

Because all classes in the .NET Framework are derived from Object, every method defined in the Object class is available in all objects in the system. Derived classes can and do override some of these methods, including:

Equals - Supports comparisons between objects.
Finalize - Performs cleanup operations before an object is automatically reclaimed.
GetHashCode - Generates a number corresponding to the value of the object to support the use of a hash table.
ToString - Manufactures a human-readable text string that describes an instance of the class.

Performance Considerations

If you are designing a class, such as a collection, that must handle any type of object, you can create class members that accept instances of the Object class. However, the process of boxing and unboxing a type carries a performance cost. If you know your new class will frequently handle certain value types you can use one of two tactics to minimize the cost of boxing.

One tactic is to create a general method that accepts an Object type, and a set of type-specific method overloads that accept each value type you expect your class to frequently handle. If a type-specific method exists that accepts the calling parameter type, no boxing occurs and the type-specific method is invoked. If there is no method argument that matches the calling parameter type, the parameter is boxed and the general method is invoked.
The other tactic is to design your class and its methods to use generics. The common language runtime creates a closed generic type when you create an instance of your class and specify a generic type argument. The generic method is type-specific and can be invoked without boxing the calling parameter.

Although it is sometimes necessary to develop general purpose classes that accept and return Object types, you can improve performance by also providing a type-specific class to handle a frequently used type. For example, providing a class that is specific to setting and getting Boolean values eliminates the cost of boxing and unboxing Boolean values.

Examples

The following example defines a Point type derived from the Object class and overrides many of the virtual methods of the Object class. In addition, the example shows how to call many of the static and instance methods of the Object class.

Note:
To run this example, see Building Examples That Use a Demo Method and a TextBlock Control.


' The Point class is derived from System.Object.

Class Point
    Public x, y As Integer

    Public Sub New(ByVal x As Integer, ByVal y As Integer)
        Me.x = x
        Me.y = y
    End Sub

    Public Overrides Function Equals(ByVal obj As Object) As Boolean
        ' If Me and obj do not refer to the same type, then they are not equal.
        Dim objType As Type = obj.GetType()
        Dim meType As Type = Me.GetType()
        If Not objType.Equals(meType) Then
            Return False
        End If
        ' Return true if  x and y fields match.
        Dim other As Point = CType(obj, Point)
        Return Me.x = other.x AndAlso Me.y = other.y
    End Function

    ' Return the XOR of the x and y fields.
    Public Overrides Function GetHashCode() As Integer
        Return x Xor y
    End Function

    ' Return the point's value as a string.
    Public Overrides Function ToString() As String
        Return String.Format("({0}, {1})", x, y)
    End Function

    ' Return a copy of this point object by making a simple field copy.
    Public Function Copy() As Point
        Return CType(Me.MemberwiseClone(), Point)
    End Function
End Class

Public NotInheritable Class Example

    Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
        ' Construct a Point object.
        Dim p1 As New Point(1, 2)

        ' Make another Point object that is a copy of the first.
        Dim p2 As Point = p1.Copy()

        ' Make another variable that references the first Point object.
        Dim p3 As Point = p1

        ' The line below displays false because p1 and p2 refer to two different objects.
        outputBlock.Text += Object.ReferenceEquals(p1, p2).ToString() & vbCrLf

        ' The line below displays true because p1 and p2 refer to two different objects 
        ' that have the same value.
        outputBlock.Text += Object.Equals(p1, p2) & vbCrLf

        ' The line below displays true because p1 and p3 refer to one object.
        outputBlock.Text += Object.ReferenceEquals(p1, p3) & vbCrLf

        ' The line below displays: p1's value is: (1, 2)
        outputBlock.Text += String.Format("p1's value is: {0}", p1.ToString()) & vbCrLf

    End Sub
End Class

' This code example produces the following output:
'
' False
' True
' True
' p1's value is: (1, 2)
'

// The Point class is derived from System.Object.
class Point
{
    public int x, y;

    public Point(int x, int y)
    {
        this.x = x;
        this.y = y;
    }

    public override bool Equals(object obj)
    {
        // If this and obj do not refer to the same type, then they are not equal.
        if (obj.GetType() != this.GetType()) return false;

        // Return true if  x and y fields match.
        Point other = (Point)obj;
        return (this.x == other.x) && (this.y == other.y);
    }

    // Return the XOR of the x and y fields.
    public override int GetHashCode()
    {
        return x ^ y;
    }

    // Return the point's value as a string.
    public override string ToString()
    {
        return String.Format("({0}, {1})", x, y);
    }

    // Return a copy of this point object by making a simple field copy.
    public Point Copy()
    {
        return (Point)this.MemberwiseClone();
    }
}

public sealed class Example
{
    public static void Demo(System.Windows.Controls.TextBlock outputBlock)
    {
        // Construct a Point object.
        Point p1 = new Point(1, 2);

        // Make another Point object that is a copy of the first.
        Point p2 = p1.Copy();

        // Make another variable that references the first Point object.
        Point p3 = p1;

        // The line below displays false because
        // p1 and p2 refer to two different objects.
        outputBlock.Text += Object.ReferenceEquals(p1, p2).ToString() + "\n";

        // The line below displays true because p1 and p2
        // refer to two different objects that have the same value.
        outputBlock.Text += Object.Equals(p1, p2).ToString() + "\n";

        // The line below displays true because p1 and p3 refer to one object.
        outputBlock.Text += Object.ReferenceEquals(p1, p3).ToString() + "\n";

        // The line below displays: p1's value is: (1, 2)
        outputBlock.Text += String.Format("p1's value is: {0}", p1.ToString()) + "\n";
    }
}

// This code example produces the following output:
//
// False
// True
// True
// p1's value is: (1, 2)
//

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

Public static (Shared in Visual Basic) members of this type are thread safe. Instance members are not guaranteed to be thread-safe.

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