C# 0 The Complete Reference

PART II

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C o l l e c t i o n s ,   E n u m e r a t o r s ,   a n d   I t e r a t o r s    

795

The following program demonstrates 

Stack

:

// Demonstrate the Stack class.

using System;

using System.Collections.Generic;

class GenStackDemo {

  static void Main() {

    Stack st = new Stack();

    st.Push("One");

    st.Push("Two");

    st.Push("Three");

    st.Push("Four");

    st.Push("Five");

    while(st.Count > 0) {

      string str = st.Pop();

      Console.Write(str + " ");

    }

    Console.WriteLine();

  }

}

The output is shown here:

Five Four Three Two One

The Queue Class

Queue

is the generic equivalent of the non-generic 

Queue

 class. It supports a first-in, 

first-out list. 

Queue

 implements the 

ICollection

,

IEnumerable

, and 

IEnumerable

interfaces.

Queue

 directly implements the 

Clear( )

,

Contains( )

, and 

CopyTo( )

 methods 

Method

Description

public T Peek( )

Returns the element on the top of the stack, but does not 

remove it.

public T Pop( )

Returns the element on the top of the stack, removing it in the 

process.

public void Push(T 

v

)

Pushes 

v

 onto the stack. 

public T[ ] ToArray( )

Returns an array that contains copies of the elements of the 

invoking stack.

public void TrimExcess( )

Removes the excess capacity of the invoking stack.

T

ABLE

 24-19 

The Methods Defi ned by 

Stack

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defined by 

ICollection

. (The 

Add( ) 

and

Remove( )

 methods are not supported, nor is 

the

IsReadOnly

 property.) 

Queue

 is a dynamic collection that grows as needed to 

accommodate the elements it must store. It defines the following constructors:

public Queue( )

public Queue(int 

capacity

)

public Queue(IEnumerable 

c

)

The first form creates an empty queue with an initial default capacity. The second form 

creates an empty queue with the initial capacity specified by 

capacity.

 The third form creates 

a queue that contains the elements of the collection specified by 

c.

In addition to the methods defined by the interfaces that it implements (and those 

methods defined by 

ICollection

 that it implements on its own), 

Queue

 defines the 

methods shown in Table 24-20. 

Queue

works just like its non-generic counterpart. To 

put an object in the queue, call 

Enqueue( )

. To remove and return the object at the front of 

the queue, call 

Dequeue( )

. You can use 

Peek( )

 to return, but not remove, the next object. 

An

InvalidOperationException

 is thrown if you call 

Dequeue( )

 or 

Peek( )

 when the 

invoking queue is empty.

Here is an example that demonstrates 

Queue

:

// Demonstrate the Queue class.

using System;

using System.Collections.Generic;

class GenQueueDemo {

  static void Main() {

    Queue q = new Queue();

    q.Enqueue(98.6);

    q.Enqueue(212.0);

    q.Enqueue(32.0);

    q.Enqueue(3.1416);

    double sum = 0.0;

    Console.Write("Queue contents: ");

    while(q.Count > 0) {

      double val = q.Dequeue();

      Console.Write(val + " ");

      sum += val;

    }

    Console.WriteLine("\nTotal is " + sum);

  }

}

The output is shown here:

Queue contents: 98.6 212 32 3.1416

Total is 345.7416

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