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The value of the current item at the beginning of the current Queue is returned, but not removed from the Queue. Use of DeQueue returns the value and removes the item from teh Queue.
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| Microsoft MSDN Links |
System.Collections
System.Collections.Queue
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| Illustrating how Peek does not update the Queue |
// Full Unit code.
// -------------------------------------------------------------
// Create a new WinForm application, double click the form to
// create an OnLoad event, and then replace the WinForm unit
// with this text.
unit WinForm;
interface
uses
System.Drawing, System.Collections, System.ComponentModel,
System.Windows.Forms, System.Data;
type
TWinForm = class(System.Windows.Forms.Form)
\{REGION 'Designer Managed Code'\} // Note that REGION and ENREGION should be prefixed by a dollar sign
strict private
///
/// Required designer variable.
///
Components: System.ComponentModel.Container;
///
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
///
procedure InitializeComponent;
procedure TWinForm_Load(sender: System.Object; e: System.EventArgs);
{ENDREGION}
strict protected
///
/// Clean up any resources being used.
///
procedure Dispose(Disposing: Boolean); override;
private
{ Private Declarations }
public
constructor Create;
end;
[assembly: RuntimeRequiredAttribute(TypeOf(TWinForm))]
implementation
\{REGION 'Windows Form Designer generated code'\}
///
/// Required method for Designer support -- do not modify
/// the contents of this method with the code editor.
///
procedure TWinForm.InitializeComponent;
begin
//
// TWinForm
//
Self.AutoScaleBaseSize := System.Drawing.Size.Create(5, 13);
Self.ClientSize := System.Drawing.Size.Create(292, 266);
Self.Name := 'TWinForm';
Self.Text := 'WinForm';
Include(Self.Load, Self.TWinForm_Load);
end;
{ENDREGION}
procedure TWinForm.Dispose(Disposing: Boolean);
begin
if Disposing then
begin
if Components <> nil then
Components.Dispose();
end;
inherited Dispose(Disposing);
end;
constructor TWinForm.Create;
begin
inherited Create;
//
// Required for Windows Form Designer support
//
InitializeComponent;
//
// TODO: Add any constructor code after InitializeComponent call
//
end;
procedure TWinForm.TWinForm_Load(sender: System.Object; e: System.EventArgs);
program Project1;
{$APPTYPE CONSOLE}
uses
System.Collections;
var
MyQueue : System.Collections.Queue;
Enumerator : IEnumerator;
begin
// Create our queue
MyQueue := Queue.Create;
// Add entries to the queue
MyQueue.EnQueue('First');
MyQueue.EnQueue('Second');
MyQueue.Enqueue('Third');
// Display the queue
Console.WriteLine('Queue contains :');
Console.WriteLine;
Enumerator := MyQueue.GetEnumerator;
while enumerator.MoveNext do
Console.WriteLine(Enumerator.Current.ToString);
// Show the next item to be DeQueued
Console.WriteLine;
Console.WriteLine('Peeking at the next item to be DeQueued :');
Console.WriteLine;
Console.WriteLine(MyQueue.Peek.ToString);
Console.WriteLine;
Console.WriteLine('Show that the Queue is unaffacted :');
Console.WriteLine;
Enumerator := MyQueue.GetEnumerator;
while enumerator.MoveNext do
Console.WriteLine(Enumerator.Current.ToString);
Console.Readline;
end.
end. | | Hide full unit code | Queue contains :
First
Second
Third
Peeking at the next item to be DeQueued :
First
Show that the Queue is unaffacted :
First
Second
Third
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