Queue<T>.Contains(T) 方法

定义

命名空间:

System.Collections.Generic

程序集:

System.Collections.dll

程序集:

System.dll

程序集:

netstandard.dll

确定某元素是否在 Queue<T> 中。

public:
 bool Contains(T item);

public bool Contains (T item);

member this.Contains : 'T -> bool

Public Function Contains (item As T) As Boolean

参数

item

T

要在 Queue<T> 中定位的对象。 对于引用类型，该值可以为 null。

返回

Boolean

如果在 true 中找到 item，则为 Queue<T>；否则为 false。

示例

下面的代码示例演示泛型类的 Queue<T> 多个方法，包括该方法 Contains 。

代码示例创建具有默认容量的字符串队列，并使用 Enqueue 该方法对五个字符串进行排队。 枚举队列的元素，不会更改队列的状态。 该方法 Dequeue 用于取消第一个字符串的排队。 该方法 Peek 用于查看队列中的下一项，然后使用 Dequeue 该方法取消排队。

该方法 ToArray 用于创建数组并将队列元素复制到该数组，然后将该数组传递给 Queue<T> 采用 IEnumerable<T>的构造函数，创建队列的副本。 将显示副本的元素。

创建队列大小两次的数组，该方法 CopyTo 用于复制从数组中间开始的数组元素。 构造 Queue<T> 函数再次用于创建队列的第二个副本，该副本在开头包含三个 null 元素。

该方法 Contains 用于显示字符串“四”位于队列的第一个副本中，之后 Clear 该方法将清除副本，属性 Count 显示队列为空。

using System;
using System.Collections.Generic;

class Example
{
    public static void Main()
    {
        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 )
        {
            Console.WriteLine(number);
        }

        Console.WriteLine("\nDequeuing '{0}'", numbers.Dequeue());
        Console.WriteLine("Peek at next item to dequeue: {0}",
            numbers.Peek());
        Console.WriteLine("Dequeuing '{0}'", numbers.Dequeue());

        // 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());

        Console.WriteLine("\nContents of the first copy:");
        foreach( string number in queueCopy )
        {
            Console.WriteLine(number);
        }

        // 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);

        Console.WriteLine("\nContents of the second copy, with duplicates and nulls:");
        foreach( string number in queueCopy2 )
        {
            Console.WriteLine(number);
        }

        Console.WriteLine("\nqueueCopy.Contains(\"four\") = {0}",
            queueCopy.Contains("four"));

        Console.WriteLine("\nqueueCopy.Clear()");
        queueCopy.Clear();
        Console.WriteLine("\nqueueCopy.Count = {0}", queueCopy.Count);
    }
}

/* 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 first 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
 */

Imports System.Collections.Generic

Module Example

    Sub Main

        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
            Console.WriteLine(number)
        Next

        Console.WriteLine(vbLf & "Dequeuing '{0}'", numbers.Dequeue())
        Console.WriteLine("Peek at next item to dequeue: {0}", _
            numbers.Peek())    
        Console.WriteLine("Dequeuing '{0}'", numbers.Dequeue())

        ' 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())

        Console.WriteLine(vbLf & "Contents of the first copy:")
        For Each number As String In queueCopy
            Console.WriteLine(number)
        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)

        Console.WriteLine(vbLf & _
            "Contents of the second copy, with duplicates and nulls:")
        For Each number As String In queueCopy2
            Console.WriteLine(number)
        Next

        Console.WriteLine(vbLf & "queueCopy.Contains(""four"") = {0}", _
            queueCopy.Contains("four"))

        Console.WriteLine(vbLf & "queueCopy.Clear()")
        queueCopy.Clear()
        Console.WriteLine(vbLf & "queueCopy.Count = {0}", _
            queueCopy.Count)
    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

注解

此方法使用队列中值类型的默认相等比较器EqualityComparer<T>.DefaultT确定相等性。

此方法执行线性搜索;因此，此方法是 O () n 操作，其中n。Count

另请参阅

• 执行不区分区域性的字符串操作