Stack Class

Stack Class

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Namespace

System.Collections (standard version)

System.Collections.Generic (generic version)

Creatable

Yes

Description

The Stack object implements a "last in, first out" (LIFO) data structure. Items are added to the top of the stack, and new items are placed "on top" of the previously added items. Only the current topmost item can be removed. A real-life parallel would be a stack of books or a stack of pancakes.

The stack includes features for adding items (Push), removing items (Pop), and counting the items in the stack (Count), among other features. Objects of any type may be added to the stack.

The following table lists some of the more useful and interesting members of the Stack class. Those marked with an asterisk (*) have separate entries in this chapter.

Member	Description
Clear Method	Removes all items from the stack
Clone Method	Makes a distinct copy of the stack and its members
Contains Method *	Indicates whether a specific object is on the stack
CopyTo Method *	Copies stack elements to an existing array
Count Property	Indicates the number of items currently on the stack
IsReadOnly Property	Indicates whether the stack is read-only or not
Peek Method *	Returns the top stack item without removing it
Pop Method *	Removes and returns the top item on the stack
Push Method *	Adds a new item to the top of the stack
ToArray Method*	Copies the stack to a new array

Example

This sample code shows the basic use of the stack.

     ' ----- Add some basic items to a stack.     Dim nameStack As New Stack     nameStack.Push("Chopin")     nameStack.Push("Mozart")     nameStack.Push("Beethoven")     ' ----- Examine and return the items.     MsgBox(nameStack.Peek(  ))   ' Displays "Beethoven"     MsgBox(nameStack.Pop(  ))    ' Displays "Beethoven"     MsgBox(nameStack.Pop(  ))    ' Displays "Mozart"     ' ----- Remove the remaining items.     MsgBox(nameStack.Count)    ' Displays 1 (for Chopin)     nameStack.Clear(  ) 

Version Differences

Visual Basic 2005 adds support for generics to several collection-style classes, including the Stack class. The version of the Stack class that supports generics appears in the System.Collections.Generic namespace. Generics are discussed in Chapter 10.

See Also

Collection Class, Hashtable Class, Queue Class