Articolo
11/18/2011

Queue<T> Class

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Represents a first-in, first-out collection of objects.

Inheritance Hierarchy

System.Object
System.Collections.Generic.Queue<T>

Namespace: System.Collections.Generic
Assembly: System (in System.dll)

Syntax

'Declaration
<ComVisibleAttribute(False)> _
<DebuggerDisplayAttribute("Count = {Count}")> _
Public Class Queue(Of T) _
    Implements IEnumerable(Of T), ICollection, IEnumerable

[ComVisibleAttribute(false)]
[DebuggerDisplayAttribute("Count = {Count}")]
public class Queue<T> : IEnumerable<T>, ICollection, 
    IEnumerable

Type Parameters

T
Specifies the type of elements in the queue.

The Queue<T> type exposes the following members.

Constructors

	Name	Description
	Queue<T>()	Initializes a new instance of the Queue<T> class that is empty and has the default initial capacity.
	Queue<T>(IEnumerable<T>)	Initializes a new instance of the Queue<T> class that contains elements copied from the specified collection and has sufficient capacity to accommodate the number of elements copied.
	Queue<T>(Int32)	Initializes a new instance of the Queue<T> class that is empty and has the specified initial capacity.

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Properties

	Name	Description
	Count	Gets the number of elements contained in the Queue<T>.

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Methods

	Name	Description
	Clear	Removes all objects from the Queue<T>.
	Contains	Determines whether an element is in the Queue<T>.
	CopyTo	Copies the Queue<T> elements to an existing one-dimensional Array, starting at the specified array index.
	Dequeue	Removes and returns the object at the beginning of the Queue<T>.
	Enqueue	Adds an object to the end of the Queue<T>.
	Equals(Object)	Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetEnumerator	Returns an enumerator that iterates through the Queue<T>.
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	Peek	Returns the object at the beginning of the Queue<T> without removing it.
	ToArray	Copies the Queue<T> elements to a new array.
	ToString	Returns a string that represents the current object. (Inherited from Object.)
	TrimExcess	Sets the capacity to the actual number of elements in the Queue<T>, if that number is less than 90 percent of current capacity.

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Extension Methods

	Name	Description
	Aggregate<T>(Func<T, T, T>)	Overloaded. Applies an accumulator function over a sequence. (Defined by Enumerable.)
	Aggregate<T, TAccumulate>(TAccumulate, Func<TAccumulate, T, TAccumulate>)	Overloaded. Applies an accumulator function over a sequence. The specified seed value is used as the initial accumulator value. (Defined by Enumerable.)
	Aggregate<T, TAccumulate, TResult>(TAccumulate, Func<TAccumulate, T, TAccumulate>, Func<TAccumulate, TResult>)	Overloaded. Applies an accumulator function over a sequence. The specified seed value is used as the initial accumulator value, and the specified function is used to select the result value. (Defined by Enumerable.)
	All<T>	Determines whether all elements of a sequence satisfy a condition. (Defined by Enumerable.)
	Any<T>()	Overloaded. Determines whether a sequence contains any elements. (Defined by Enumerable.)
	Any<T>(Func<T, Boolean>)	Overloaded. Determines whether any element of a sequence satisfies a condition. (Defined by Enumerable.)
	AsEnumerable<T>	Returns the input typed as IEnumerable<T>. (Defined by Enumerable.)
	AsQueryable()	Overloaded. Converts an IEnumerable to an IQueryable. (Defined by Queryable.)
	AsQueryable<T>()	Overloaded. Converts a generic IEnumerable<T> to a generic IQueryable<T>. (Defined by Queryable.)
	Average<T>(Func<T, Decimal>)	Overloaded. Computes the average of a sequence of Decimal values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<T>(Func<T, Nullable<Decimal>>)	Overloaded. Computes the average of a sequence of nullable Decimal values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<T>(Func<T, Double>)	Overloaded. Computes the average of a sequence of Double values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<T>(Func<T, Nullable<Double>>)	Overloaded. Computes the average of a sequence of nullable Double values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<T>(Func<T, Int32>)	Overloaded. Computes the average of a sequence of Int32 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<T>(Func<T, Nullable<Int32>>)	Overloaded. Computes the average of a sequence of nullable Int32 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<T>(Func<T, Int64>)	Overloaded. Computes the average of a sequence of Int64 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<T>(Func<T, Nullable<Int64>>)	Overloaded. Computes the average of a sequence of nullable Int64 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<T>(Func<T, Single>)	Overloaded. Computes the average of a sequence of Single values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<T>(Func<T, Nullable<Single>>)	Overloaded. Computes the average of a sequence of nullable Single values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Cast<TResult>	Converts the elements of an IEnumerable to the specified type. (Defined by Enumerable.)
	Concat<T>	Concatenates two sequences. (Defined by Enumerable.)
	Contains<T>(T)	Overloaded. Determines whether a sequence contains a specified element by using the default equality comparer. (Defined by Enumerable.)
	Contains<T>(T, IEqualityComparer<T>)	Overloaded. Determines whether a sequence contains a specified element by using a specified IEqualityComparer<T>. (Defined by Enumerable.)
	Count<T>()	Overloaded. Returns the number of elements in a sequence. (Defined by Enumerable.)
	Count<T>(Func<T, Boolean>)	Overloaded. Returns a number that represents how many elements in the specified sequence satisfy a condition. (Defined by Enumerable.)
	DefaultIfEmpty<T>()	Overloaded. Returns the elements of the specified sequence or the type parameter's default value in a singleton collection if the sequence is empty. (Defined by Enumerable.)
	DefaultIfEmpty<T>(T)	Overloaded. Returns the elements of the specified sequence or the specified value in a singleton collection if the sequence is empty. (Defined by Enumerable.)
	Distinct<T>()	Overloaded. Returns distinct elements from a sequence by using the default equality comparer to compare values. (Defined by Enumerable.)
	Distinct<T>(IEqualityComparer<T>)	Overloaded. Returns distinct elements from a sequence by using a specified IEqualityComparer<T> to compare values. (Defined by Enumerable.)
	ElementAt<T>	Returns the element at a specified index in a sequence. (Defined by Enumerable.)
	ElementAtOrDefault<T>	Returns the element at a specified index in a sequence or a default value if the index is out of range. (Defined by Enumerable.)
	Except<T>(IEnumerable<T>)	Overloaded. Produces the set difference of two sequences by using the default equality comparer to compare values. (Defined by Enumerable.)
	Except<T>(IEnumerable<T>, IEqualityComparer<T>)	Overloaded. Produces the set difference of two sequences by using the specified IEqualityComparer<T> to compare values. (Defined by Enumerable.)
	First<T>()	Overloaded. Returns the first element of a sequence. (Defined by Enumerable.)
	First<T>(Func<T, Boolean>)	Overloaded. Returns the first element in a sequence that satisfies a specified condition. (Defined by Enumerable.)
	FirstOrDefault<T>()	Overloaded. Returns the first element of a sequence, or a default value if the sequence contains no elements. (Defined by Enumerable.)
	FirstOrDefault<T>(Func<T, Boolean>)	Overloaded. Returns the first element of the sequence that satisfies a condition or a default value if no such element is found. (Defined by Enumerable.)
	GroupBy<T, TKey>(Func<T, TKey>)	Overloaded. Groups the elements of a sequence according to a specified key selector function. (Defined by Enumerable.)
	GroupBy<T, TKey>(Func<T, TKey>, IEqualityComparer<TKey>)	Overloaded. Groups the elements of a sequence according to a specified key selector function and compares the keys by using a specified comparer. (Defined by Enumerable.)
	GroupBy<T, TKey, TElement>(Func<T, TKey>, Func<T, TElement>)	Overloaded. Groups the elements of a sequence according to a specified key selector function and projects the elements for each group by using a specified function. (Defined by Enumerable.)
	GroupBy<T, TKey, TResult>(Func<T, TKey>, Func<TKey, IEnumerable<T>, TResult>)	Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. (Defined by Enumerable.)
	GroupBy<T, TKey, TElement>(Func<T, TKey>, Func<T, TElement>, IEqualityComparer<TKey>)	Overloaded. Groups the elements of a sequence according to a key selector function. The keys are compared by using a comparer and each group's elements are projected by using a specified function. (Defined by Enumerable.)
	GroupBy<T, TKey, TResult>(Func<T, TKey>, Func<TKey, IEnumerable<T>, TResult>, IEqualityComparer<TKey>)	Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. The keys are compared by using a specified comparer. (Defined by Enumerable.)
	GroupBy<T, TKey, TElement, TResult>(Func<T, TKey>, Func<T, TElement>, Func<TKey, IEnumerable<TElement>, TResult>)	Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. The elements of each group are projected by using a specified function. (Defined by Enumerable.)
	GroupBy<T, TKey, TElement, TResult>(Func<T, TKey>, Func<T, TElement>, Func<TKey, IEnumerable<TElement>, TResult>, IEqualityComparer<TKey>)	Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. Key values are compared by using a specified comparer, and the elements of each group are projected by using a specified function. (Defined by Enumerable.)
	GroupJoin<T, TInner, TKey, TResult>(IEnumerable<TInner>, Func<T, TKey>, Func<TInner, TKey>, Func<T, IEnumerable<TInner>, TResult>)	Overloaded. Correlates the elements of two sequences based on equality of keys and groups the results. The default equality comparer is used to compare keys. (Defined by Enumerable.)
	GroupJoin<T, TInner, TKey, TResult>(IEnumerable<TInner>, Func<T, TKey>, Func<TInner, TKey>, Func<T, IEnumerable<TInner>, TResult>, IEqualityComparer<TKey>)	Overloaded. Correlates the elements of two sequences based on key equality and groups the results. A specified IEqualityComparer<T> is used to compare keys. (Defined by Enumerable.)
	Intersect<T>(IEnumerable<T>)	Overloaded. Produces the set intersection of two sequences by using the default equality comparer to compare values. (Defined by Enumerable.)
	Intersect<T>(IEnumerable<T>, IEqualityComparer<T>)	Overloaded. Produces the set intersection of two sequences by using the specified IEqualityComparer<T> to compare values. (Defined by Enumerable.)
	Join<T, TInner, TKey, TResult>(IEnumerable<TInner>, Func<T, TKey>, Func<TInner, TKey>, Func<T, TInner, TResult>)	Overloaded. Correlates the elements of two sequences based on matching keys. The default equality comparer is used to compare keys. (Defined by Enumerable.)
	Join<T, TInner, TKey, TResult>(IEnumerable<TInner>, Func<T, TKey>, Func<TInner, TKey>, Func<T, TInner, TResult>, IEqualityComparer<TKey>)	Overloaded. Correlates the elements of two sequences based on matching keys. A specified IEqualityComparer<T> is used to compare keys. (Defined by Enumerable.)
	Last<T>()	Overloaded. Returns the last element of a sequence. (Defined by Enumerable.)
	Last<T>(Func<T, Boolean>)	Overloaded. Returns the last element of a sequence that satisfies a specified condition. (Defined by Enumerable.)
	LastOrDefault<T>()	Overloaded. Returns the last element of a sequence, or a default value if the sequence contains no elements. (Defined by Enumerable.)
	LastOrDefault<T>(Func<T, Boolean>)	Overloaded. Returns the last element of a sequence that satisfies a condition or a default value if no such element is found. (Defined by Enumerable.)
	LongCount<T>()	Overloaded. Returns an Int64 that represents the total number of elements in a sequence. (Defined by Enumerable.)
	LongCount<T>(Func<T, Boolean>)	Overloaded. Returns an Int64 that represents how many elements in a sequence satisfy a condition. (Defined by Enumerable.)
	Max<T>()	Overloaded. Returns the maximum value in a generic sequence. (Defined by Enumerable.)
	Max<T>(Func<T, Decimal>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Decimal value. (Defined by Enumerable.)
	Max<T>(Func<T, Nullable<Decimal>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Decimal value. (Defined by Enumerable.)
	Max<T>(Func<T, Double>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Double value. (Defined by Enumerable.)
	Max<T>(Func<T, Nullable<Double>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Double value. (Defined by Enumerable.)
	Max<T>(Func<T, Int32>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Int32 value. (Defined by Enumerable.)
	Max<T>(Func<T, Nullable<Int32>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Int32 value. (Defined by Enumerable.)
	Max<T>(Func<T, Int64>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Int64 value. (Defined by Enumerable.)
	Max<T>(Func<T, Nullable<Int64>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Int64 value. (Defined by Enumerable.)
	Max<T>(Func<T, Single>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Single value. (Defined by Enumerable.)
	Max<T>(Func<T, Nullable<Single>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Single value. (Defined by Enumerable.)
	Max<T, TResult>(Func<T, TResult>)	Overloaded. Invokes a transform function on each element of a generic sequence and returns the maximum resulting value. (Defined by Enumerable.)
	Min<T>()	Overloaded. Returns the minimum value in a generic sequence. (Defined by Enumerable.)
	Min<T>(Func<T, Decimal>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Decimal value. (Defined by Enumerable.)
	Min<T>(Func<T, Nullable<Decimal>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Decimal value. (Defined by Enumerable.)
	Min<T>(Func<T, Double>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Double value. (Defined by Enumerable.)
	Min<T>(Func<T, Nullable<Double>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Double value. (Defined by Enumerable.)
	Min<T>(Func<T, Int32>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Int32 value. (Defined by Enumerable.)
	Min<T>(Func<T, Nullable<Int32>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Int32 value. (Defined by Enumerable.)
	Min<T>(Func<T, Int64>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Int64 value. (Defined by Enumerable.)
	Min<T>(Func<T, Nullable<Int64>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Int64 value. (Defined by Enumerable.)
	Min<T>(Func<T, Single>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Single value. (Defined by Enumerable.)
	Min<T>(Func<T, Nullable<Single>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Single value. (Defined by Enumerable.)
	Min<T, TResult>(Func<T, TResult>)	Overloaded. Invokes a transform function on each element of a generic sequence and returns the minimum resulting value. (Defined by Enumerable.)
	OfType<TResult>	Filters the elements of an IEnumerable based on a specified type. (Defined by Enumerable.)
	OrderBy<T, TKey>(Func<T, TKey>)	Overloaded. Sorts the elements of a sequence in ascending order according to a key. (Defined by Enumerable.)
	OrderBy<T, TKey>(Func<T, TKey>, IComparer<TKey>)	Overloaded. Sorts the elements of a sequence in ascending order by using a specified comparer. (Defined by Enumerable.)
	OrderByDescending<T, TKey>(Func<T, TKey>)	Overloaded. Sorts the elements of a sequence in descending order according to a key. (Defined by Enumerable.)
	OrderByDescending<T, TKey>(Func<T, TKey>, IComparer<TKey>)	Overloaded. Sorts the elements of a sequence in descending order by using a specified comparer. (Defined by Enumerable.)
	Reverse<T>	Inverts the order of the elements in a sequence. (Defined by Enumerable.)
	Select<T, TResult>(Func<T, TResult>)	Overloaded. Projects each element of a sequence into a new form. (Defined by Enumerable.)
	Select<T, TResult>(Func<T, Int32, TResult>)	Overloaded. Projects each element of a sequence into a new form by incorporating the element's index. (Defined by Enumerable.)
	SelectMany<T, TResult>(Func<T, IEnumerable<TResult>>)	Overloaded. Projects each element of a sequence to an IEnumerable<T> and flattens the resulting sequences into one sequence. (Defined by Enumerable.)
	SelectMany<T, TResult>(Func<T, Int32, IEnumerable<TResult>>)	Overloaded. Projects each element of a sequence to an IEnumerable<T>, and flattens the resulting sequences into one sequence. The index of each source element is used in the projected form of that element. (Defined by Enumerable.)
	SelectMany<T, TCollection, TResult>(Func<T, Int32, IEnumerable<TCollection>>, Func<T, TCollection, TResult>)	Overloaded. Projects each element of a sequence to an IEnumerable<T>, flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein. The index of each source element is used in the intermediate projected form of that element. (Defined by Enumerable.)
	SelectMany<T, TCollection, TResult>(Func<T, IEnumerable<TCollection>>, Func<T, TCollection, TResult>)	Overloaded. Projects each element of a sequence to an IEnumerable<T>, flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein. (Defined by Enumerable.)
	SequenceEqual<T>(IEnumerable<T>)	Overloaded. Determines whether two sequences are equal by comparing the elements by using the default equality comparer for their type. (Defined by Enumerable.)
	SequenceEqual<T>(IEnumerable<T>, IEqualityComparer<T>)	Overloaded. Determines whether two sequences are equal by comparing their elements by using a specified IEqualityComparer<T>. (Defined by Enumerable.)
	Single<T>()	Overloaded. Returns the only element of a sequence, and throws an exception if there is not exactly one element in the sequence. (Defined by Enumerable.)
	Single<T>(Func<T, Boolean>)	Overloaded. Returns the only element of a sequence that satisfies a specified condition, and throws an exception if more than one such element exists. (Defined by Enumerable.)
	SingleOrDefault<T>()	Overloaded. Returns the only element of a sequence, or a default value if the sequence is empty; this method throws an exception if there is more than one element in the sequence. (Defined by Enumerable.)
	SingleOrDefault<T>(Func<T, Boolean>)	Overloaded. Returns the only element of a sequence that satisfies a specified condition or a default value if no such element exists; this method throws an exception if more than one element satisfies the condition. (Defined by Enumerable.)
	Skip<T>	Bypasses a specified number of elements in a sequence and then returns the remaining elements. (Defined by Enumerable.)
	SkipWhile<T>(Func<T, Boolean>)	Overloaded. Bypasses elements in a sequence as long as a specified condition is true and then returns the remaining elements. (Defined by Enumerable.)
	SkipWhile<T>(Func<T, Int32, Boolean>)	Overloaded. Bypasses elements in a sequence as long as a specified condition is true and then returns the remaining elements. The element's index is used in the logic of the predicate function. (Defined by Enumerable.)
	Sum<T>(Func<T, Decimal>)	Overloaded. Computes the sum of the sequence of Decimal values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<T>(Func<T, Nullable<Decimal>>)	Overloaded. Computes the sum of the sequence of nullable Decimal values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<T>(Func<T, Double>)	Overloaded. Computes the sum of the sequence of Double values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<T>(Func<T, Nullable<Double>>)	Overloaded. Computes the sum of the sequence of nullable Double values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<T>(Func<T, Int32>)	Overloaded. Computes the sum of the sequence of Int32 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<T>(Func<T, Nullable<Int32>>)	Overloaded. Computes the sum of the sequence of nullable Int32 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<T>(Func<T, Int64>)	Overloaded. Computes the sum of the sequence of Int64 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<T>(Func<T, Nullable<Int64>>)	Overloaded. Computes the sum of the sequence of nullable Int64 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<T>(Func<T, Single>)	Overloaded. Computes the sum of the sequence of Single values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<T>(Func<T, Nullable<Single>>)	Overloaded. Computes the sum of the sequence of nullable Single values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Take<T>	Returns a specified number of contiguous elements from the start of a sequence. (Defined by Enumerable.)
	TakeWhile<T>(Func<T, Boolean>)	Overloaded. Returns elements from a sequence as long as a specified condition is true. (Defined by Enumerable.)
	TakeWhile<T>(Func<T, Int32, Boolean>)	Overloaded. Returns elements from a sequence as long as a specified condition is true. The element's index is used in the logic of the predicate function. (Defined by Enumerable.)
	ToArray<T>	Creates an array from a IEnumerable<T>. (Defined by Enumerable.)
	ToDictionary<T, TKey>(Func<T, TKey>)	Overloaded. Creates a Dictionary<TKey, TValue> from an IEnumerable<T> according to a specified key selector function. (Defined by Enumerable.)
	ToDictionary<T, TKey>(Func<T, TKey>, IEqualityComparer<TKey>)	Overloaded. Creates a Dictionary<TKey, TValue> from an IEnumerable<T> according to a specified key selector function and key comparer. (Defined by Enumerable.)
	ToDictionary<T, TKey, TElement>(Func<T, TKey>, Func<T, TElement>)	Overloaded. Creates a Dictionary<TKey, TValue> from an IEnumerable<T> according to specified key selector and element selector functions. (Defined by Enumerable.)
	ToDictionary<T, TKey, TElement>(Func<T, TKey>, Func<T, TElement>, IEqualityComparer<TKey>)	Overloaded. Creates a Dictionary<TKey, TValue> from an IEnumerable<T> according to a specified key selector function, a comparer, and an element selector function. (Defined by Enumerable.)
	ToList<T>	Creates a List<T> from an IEnumerable<T>. (Defined by Enumerable.)
	ToLookup<T, TKey>(Func<T, TKey>)	Overloaded. Creates a Lookup<TKey, TElement> from an IEnumerable<T> according to a specified key selector function. (Defined by Enumerable.)
	ToLookup<T, TKey>(Func<T, TKey>, IEqualityComparer<TKey>)	Overloaded. Creates a Lookup<TKey, TElement> from an IEnumerable<T> according to a specified key selector function and key comparer. (Defined by Enumerable.)
	ToLookup<T, TKey, TElement>(Func<T, TKey>, Func<T, TElement>)	Overloaded. Creates a Lookup<TKey, TElement> from an IEnumerable<T> according to specified key selector and element selector functions. (Defined by Enumerable.)
	ToLookup<T, TKey, TElement>(Func<T, TKey>, Func<T, TElement>, IEqualityComparer<TKey>)	Overloaded. Creates a Lookup<TKey, TElement> from an IEnumerable<T> according to a specified key selector function, a comparer and an element selector function. (Defined by Enumerable.)
	Union<T>(IEnumerable<T>)	Overloaded. Produces the set union of two sequences by using the default equality comparer. (Defined by Enumerable.)
	Union<T>(IEnumerable<T>, IEqualityComparer<T>)	Overloaded. Produces the set union of two sequences by using a specified IEqualityComparer<T>. (Defined by Enumerable.)
	Where<T>(Func<T, Boolean>)	Overloaded. Filters a sequence of values based on a predicate. (Defined by Enumerable.)
	Where<T>(Func<T, Int32, Boolean>)	Overloaded. Filters a sequence of values based on a predicate. Each element's index is used in the logic of the predicate function. (Defined by Enumerable.)
	Zip<T, TSecond, TResult>	Merges two sequences by using the specified predicate function. (Defined by Enumerable.)

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Explicit Interface Implementations

	Name	Description
	ICollection.CopyTo	Copies the elements of the ICollection to an Array, starting at a particular Array index.
	ICollection.IsSynchronized	Gets a value indicating whether access to the ICollection is synchronized (thread safe).
	ICollection.SyncRoot	Gets an object that can be used to synchronize access to the ICollection.
	IEnumerable<T>.GetEnumerator	Returns an enumerator that iterates through a collection.
	IEnumerable.GetEnumerator	Returns an enumerator that iterates through a collection.

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Remarks

Queues are useful for storing messages in the order they were received for sequential processing. Objects stored in a Queue<T> are inserted at one end and removed from the other.

The capacity of a Queue<T> is the number of elements the Queue<T> can hold. As elements are added to a Queue<T>, the capacity is automatically increased as required by reallocating the internal array. The capacity can be decreased by calling TrimExcess.

Queue<T> accepts nulla null reference (Nothing in Visual Basic) as a valid value for reference types and allows duplicate elements.

Examples

The following code example demonstrates several methods of the Queue<T> generic class. The code example creates a queue of strings with default capacity and uses the Enqueue method to queue five strings. The elements of the queue are enumerated, which does not change the state of the queue. The Dequeue method is used to dequeue the first string. The Peek method is used to look at the next item in the queue, and then the Dequeue method is used to dequeue it.

The ToArray method is used to create an array and copy the queue elements to it, then the array is passed to the Queue<T> constructor that takes IEnumerable<T>, creating a copy of the queue. The elements of the copy are displayed.

An array twice the size of the queue is created, and the CopyTo method is used to copy the array elements beginning at the middle of the array. The Queue<T> constructor is used again to create a second copy of the queue containing three null elements at the beginning.

The Contains method is used to show that the string "four" is in the first copy of the queue, after which the Clear method clears the copy and the Count property shows that the queue is empty.

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

Imports System.Collections.Generic

Module Example

   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

      Dim numbers As New Queue(Of String)
      numbers.Enqueue("one")
      numbers.Enqueue("two")
      numbers.Enqueue("three")
      numbers.Enqueue("four")
      numbers.Enqueue("five")

      ' A queue can be enumerated without disturbing its contents.
      For Each number As String In numbers
         outputBlock.Text &= number & vbCrLf
      Next

      outputBlock.Text &= String.Format(vbLf & "Dequeuing '{0}'", numbers.Dequeue()) & vbCrLf
      outputBlock.Text &= String.Format("Peek at next item to dequeue: {0}", _
          numbers.Peek()) & vbCrLf
      outputBlock.Text &= String.Format("Dequeuing '{0}'", numbers.Dequeue()) & vbCrLf

      ' Create a copy of the queue, using the ToArray method and the
      ' constructor that accepts an IEnumerable(Of T).
      Dim queueCopy As New Queue(Of String)(numbers.ToArray())

      outputBlock.Text &= vbLf & "Contents of the first copy:" & vbCrLf
      For Each number As String In queueCopy
         outputBlock.Text &= number & vbCrLf
      Next

      ' Create an array twice the size of the queue, compensating
      ' for the fact that Visual Basic allocates an extra array 
      ' element. Copy the elements of the queue, starting at the
      ' middle of the array. 
      Dim array2((numbers.Count * 2) - 1) As String
      numbers.CopyTo(array2, numbers.Count)

      ' Create a second queue, using the constructor that accepts an
      ' IEnumerable(Of T).
      Dim queueCopy2 As New Queue(Of String)(array2)

      outputBlock.Text &= String.Format(vbLf & _
          "Contents of the second copy, with duplicates and nulls:") & vbCrLf
      For Each number As String In queueCopy2
         outputBlock.Text &= number & vbCrLf
      Next

      outputBlock.Text &= vbLf & String.Format("queueCopy.Contains(""four"") = {0}", _
          queueCopy.Contains("four"))

      outputBlock.Text &= vbLf & "queueCopy.Clear()" & vbCrLf
      queueCopy.Clear()
      outputBlock.Text &= String.Format(vbLf & "queueCopy.Count = {0}", _
          queueCopy.Count) & vbCrLf
   End Sub
End Module

' This code example produces the following output:
'
'one
'two
'three
'four
'five
'
'Dequeuing 'one'
'Peek at next item to dequeue: two
'
'Dequeuing 'two'
'
'Contents of the copy:
'three
'four
'five
'
'Contents of the second copy, with duplicates and nulls:
'
'
'
'three
'four
'five
'
'queueCopy.Contains("four") = True
'
'queueCopy.Clear()
'
'queueCopy.Count = 0

using System;
using System.Collections.Generic;

class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      Queue<string> numbers = new Queue<string>();
      numbers.Enqueue("one");
      numbers.Enqueue("two");
      numbers.Enqueue("three");
      numbers.Enqueue("four");
      numbers.Enqueue("five");

      // A queue can be enumerated without disturbing its contents.
      foreach (string number in numbers)
      {
         outputBlock.Text += number + "\n";
      }

      outputBlock.Text += String.Format("\nDequeuing '{0}'", numbers.Dequeue()) + "\n";
      outputBlock.Text += String.Format("Peek at next item to dequeue: {0}",
          numbers.Peek()) + "\n";
      outputBlock.Text += String.Format("Dequeuing '{0}'", numbers.Dequeue()) + "\n";

      // Create a copy of the queue, using the ToArray method and the
      // constructor that accepts an IEnumerable<T>.
      Queue<string> queueCopy = new Queue<string>(numbers.ToArray());

      outputBlock.Text += "\nContents of the first copy:" + "\n";
      foreach (string number in queueCopy)
      {
         outputBlock.Text += number + "\n";
      }

      // Create an array twice the size of the queue and copy the
      // elements of the queue, starting at the middle of the 
      // array. 
      string[] array2 = new string[numbers.Count * 2];
      numbers.CopyTo(array2, numbers.Count);

      // Create a second queue, using the constructor that accepts an
      // IEnumerable(Of T).
      Queue<string> queueCopy2 = new Queue<string>(array2);

      outputBlock.Text += String.Format("\nContents of the second copy, with duplicates and nulls:") + "\n";
      foreach (string number in queueCopy2)
      {
         outputBlock.Text += number + "\n";
      }

      outputBlock.Text += String.Format("\nqueueCopy.Contains(\"four\") = {0}",
          queueCopy.Contains("four")) + "\n";

      outputBlock.Text += "\nqueueCopy.Clear()" + "\n";
      queueCopy.Clear();
      outputBlock.Text += String.Format("\nqueueCopy.Count = {0}", queueCopy.Count) + "\n";
   }
}

/* This code example produces the following output:

one
two
three
four
five

Dequeuing 'one'
Peek at next item to dequeue: two
Dequeuing 'two'

Contents of the copy:
three
four
five

Contents of the second copy, with duplicates and nulls:



three
four
five

queueCopy.Contains("four") = True

queueCopy.Clear()

queueCopy.Count = 0
 */

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. Any instance members are not guaranteed to be thread safe.

A Queue<T> can support multiple readers concurrently, as long as the collection is not modified. Even so, enumerating through a collection is intrinsically not a thread-safe procedure. To guarantee thread safety during enumeration, you can lock the collection during the entire enumeration. To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization.

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