Queue question

[Flo Powers]

Hi, I have a question about a queue class (I found this in Data Structures DeMYSTiFieD by Jim Keogh and Kend Davidson). It seems to me that when you enqueue the first element in a queue object created from this class, the first element in the array will be blank. Have I misunderstood the code or is it not utilizing the whole of the array?

Here is the code:

public class Queue
{
private static final int DEFAULT_SIZE = 10;
private int size;
private int front;
private int back;
private int [] values;

public Queue()
{
this( DEFAULT_SIZE );
}
 
public Queue( int size )
{
this.size = size;
values = new int[size];
front = 0;
back = 0;
}

public boolean isFull()
{
if( ( back + 1 ) % size == front )
return true;
else
return false;
}

public boolean isEmpty()
{
if( back == front )
return true;
else
return false;
}

public void enqueue( int x )
{
if( !isFull() )
{
back = ( back+1 ) % size;
values[back] = x;
}
}

public int dequeue()
{
if( !isEmpty() )
{
front = ( front + 1 ) % size;
return values[front];
}
return 0;
}

public int retSize()
{
return size;
}
}

Thanks,
Flo

[Mark Vedder]

You are correct. In this implementation, the zero index array element is not being utilized. Thus a queue created with a initial size of 3, only holds two items.

[Flo Powers]

Phew, I'm glad to hear I'd understood. Thanks!

Is this way of calculating the front and back of the queue (using modulo arithmetic) a fairly common implementation of a static queue? Also, are there other useful methods that you would normally expect to see in a queue class? I'm guessing the book has presented a rather barebones version in order not to obscure the essential characteristics of queues...

I realize that it might be preferable to use a linked list, though - would just like to make sure I've understood this properly.

Thanks,
flo
[ January 18, 2005: Message edited by: Flo Powers ]