Queue.Dequeue Metoda

Definice

Obor názvů:

System.Collections

Sestavení:

System.Collections.NonGeneric.dll

Zdroj:

Queue.cs

Odebere a vrátí objekt na začátku objektu Queue.

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

public virtual object? Dequeue ();

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

Public Overridable Function Dequeue () As Object

Návraty

Object

Objekt odebraný od začátku objektu Queue.

Výjimky

InvalidOperationException

Hodnota Queue je prázdná.

Příklady

Následující příklad ukazuje, jak přidat elementy do objektu Queue, odebrat elementy z objektu Queuenebo zobrazit prvek na začátku objektu Queue.

using namespace System;
using namespace System::Collections;
void PrintValues( IEnumerable^ myCollection );
int main()
{
   
   // Creates and initializes a new Queue.
   Queue^ myQ = gcnew 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 );
}

void PrintValues( IEnumerable^ myCollection )
{
   IEnumerator^ myEnum = myCollection->GetEnumerator();
   while ( myEnum->MoveNext() )
   {
      Object^ obj = safe_cast<Object^>(myEnum->Current);
      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

 */

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

Poznámky

Tato metoda je podobná Peek metodě , ale Peek nemění .Queue

null lze přidat k hodnotě Queue . Pokud chcete rozlišovat mezi hodnotou null a koncem objektu Queue, zkontrolujte Count vlastnost nebo zachyťte InvalidOperationExceptionhodnotu , která se vyvolá, když Queue je hodnota prázdná.

Tato metoda je O(1) operace.

Viz také

• Enqueue(Object)
• Peek()