Question

Revision Question

Consider the following Java class:

{

public static void main (String [ ] args)

{

ArrayQueue<Integer> queue;

queue = new ArrayQueue<Integer> () ;

Integer x, y ;

x = 3;

y = 6;

queue.offer (x) ;

queue.offer (12) ;

queue.offer (y) ;

y = queue.peek () ;

queue.poll () ;

queue. offer (x - 2) ;

queue.offer (x) ;

queue.offer (y + 4) ;

System.out.println ("Queue Elements: ") ;

while (! queue.empty() )

System.out.print (queue.poll () + " " ) ;

}

}

In the above, assume that the queue interface is defined as follows:

public interface Queue<E>

{

public boolean empty () ;

public int size () ;

public boolean offer (E x ) ;

public E peek () ;

public E poll () ;

}

and that the implementation ArrayQueue <E> is as discussed in the lectures.

What output would be produced when the main method of the TestQueue class is executed? If you think that no output is produced, write None.

Answer 1

OUTPUT:
Queue Elements:
12 6 1 3 7

EXPLANATION THROUGH COMMENTS:

public static void main(String[] args)
{
    ArrayQueue<Integer> queue;
    queue = new ArrayQueue<Integer> () ;
    Integer x, y ;
    x = 3;
    y = 6;
    queue.offer (x) ;//Inserts x = 3 into the queue. Current queue = [3]
    queue.offer (12) ;//Inserts 12 into the queue. Current queue = [3 12]
    queue.offer (y) ;//Inserts y = 6 into the queue. Current queue = [3 12 6]
    y = queue.peek () ;//Element at front of the queue is returned i.e. 3. So, y = 3. Current queue = [3 12 6]
    queue.poll () ;//Deletes and returns element at front of the queue which is 3. Current queue = [12 6]
    queue. offer (x - 2) ;//Inserts x-2 = 3-2 = 1 into the queue. Current queue = [12 6 1]
    queue.offer (x) ;//Inserts x = 3 into the queue. Current queue = [12 6 1 3]
    queue.offer (y + 4) ;//Inserts y+4 = 3+4 = 7 into the queue. Current queue = [12 6 1 3 7]
    System.out.println ("Queue Elements: ") ;
    while (! queue.empty() )//Loop till queue is not empty
        System.out.print (queue.poll () + " " ) ;//This will print 12 6 1 3 7 as poll will keep on deleting
                                                 // front elements and will return the deleted element
}