Queue.Peek Método

Definición

Espacio de nombres:

System.Collections

Ensamblados:

netstandard.dll, System.Collections.NonGeneric.dll

Source:

Queue.cs

Devuelve el objeto al principio de Queue sin quitarlo.

public:
 virtual System::Object ^ Peek();

public virtual object? Peek();

abstract member Peek : unit -> obj
override this.Peek : unit -> obj

Public Overridable Function Peek () As Object

Devoluciones

Object

Objeto al principio de .Queue

Excepciones

InvalidOperationException

está Queue vacío.

Ejemplos

En el ejemplo siguiente se muestra cómo agregar elementos a , Queuequitar elementos de Queueo ver el elemento al principio de Queue.

using System;
using System.Collections;
public class SamplesQueue  {

   public static void Main()  {

      // Creates and initializes a new Queue.
      Queue myQ = new Queue();
      myQ.Enqueue( "The" );
      myQ.Enqueue( "quick" );
      myQ.Enqueue( "brown" );
      myQ.Enqueue( "fox" );

      // Displays the Queue.
      Console.Write( "Queue values:" );
      PrintValues( myQ );

      // Removes an element from the Queue.
      Console.WriteLine( "(Dequeue)\t{0}", myQ.Dequeue() );

      // Displays the Queue.
      Console.Write( "Queue values:" );
      PrintValues( myQ );

      // Removes another element from the Queue.
      Console.WriteLine( "(Dequeue)\t{0}", myQ.Dequeue() );

      // Displays the Queue.
      Console.Write( "Queue values:" );
      PrintValues( myQ );

      // Views the first element in the Queue but does not remove it.
      Console.WriteLine( "(Peek)   \t{0}", myQ.Peek() );

      // Displays the Queue.
      Console.Write( "Queue values:" );
      PrintValues( myQ );
   }

   public static void PrintValues( IEnumerable myCollection )  {
      foreach ( Object obj in myCollection )
         Console.Write( "    {0}", obj );
      Console.WriteLine();
   }
}
/*
This code produces the following output.

Queue values:    The    quick    brown    fox
(Dequeue)       The
Queue values:    quick    brown    fox
(Dequeue)       quick
Queue values:    brown    fox
(Peek)          brown
Queue values:    brown    fox

*/

Imports System.Collections

Public Class SamplesQueue
    
    
    Public Shared Sub Main()
        
        ' Creates and initializes a new Queue.
        Dim myQ As New Queue()
        myQ.Enqueue("The")
        myQ.Enqueue("quick")
        myQ.Enqueue("brown")
        myQ.Enqueue("fox")
        
        ' Displays the Queue.
        Console.Write("Queue values:")
        PrintValues(myQ)
        
        ' Removes an element from the Queue.
        Console.WriteLine("(Dequeue)    {0}", myQ.Dequeue())
        
        ' Displays the Queue.
        Console.Write("Queue values:")
        PrintValues(myQ)
        
        ' Removes another element from the Queue.
        Console.WriteLine("(Dequeue)    {0}", myQ.Dequeue())
        
        ' Displays the Queue.
        Console.Write("Queue values:")
        PrintValues(myQ)
        
        ' Views the first element in the Queue but does not remove it.
        Console.WriteLine("(Peek)       {0}", myQ.Peek())
        
        ' Displays the Queue.
        Console.Write("Queue values:")
        PrintValues(myQ)
    End Sub

    Public Shared Sub PrintValues(myCollection As IEnumerable)
        Dim obj As [Object]
        For Each obj In  myCollection
            Console.Write("    {0}", obj)
        Next obj
        Console.WriteLine()
    End Sub

End Class


' This code produces the following output.
' 
' Queue values:    The    quick    brown    fox
' (Dequeue)    The
' Queue values:    quick    brown    fox
' (Dequeue)    quick
' Queue values:    brown    fox
' (Peek)       brown
' Queue values:    brown    fox

Comentarios

Este método es similar al Dequeue método , pero Peek no modifica .Queue

null se puede agregar a Queue como un valor. Para distinguir entre un valor NULL y el final de Queue, compruebe la Count propiedad o capture el InvalidOperationException, que se produce cuando está Queue vacío.

Este método es una O(1) operación.

Consulte también

• Enqueue(Object)
• Dequeue()