public class CircularQueue implements Queue {

    public static final int MAX_QUEUE_SIZE = 100;

    private Object[] q;
    private int front, rear;

    public CircularQueue() {
        q = new Object[ MAX_QUEUE_SIZE ];
        front = -1; // Represents the empty queue
        rear = -1; // Represents the empty queue
    }

    public boolean isEmpty() {
        return ( front == -1 );
    }

    private static int nextIndex(int index) {
        return ( index+1 ) % MAX_QUEUE_SIZE;
    }

    public boolean isFull() {
        return nextIndex( rear ) == front;
    }
    
    public void enqueue( Object o ) {
	// pre-condition:
	if ( isFull() )
	    throw new FullQueueException();

        if ( isEmpty() ) {
	    front = 0;
        }
        rear = nextIndex( rear );
        q[ rear ] = o;
    }

    public Object dequeue() {
	
	if ( isEmpty() ) 
	    throw new EmptyQueueException();

        Object result = q[front];

        if ( front == rear ) {
	    front = -1;
	    rear  = -1;
        } else {
	    front = nextIndex( front );
        }
        return result;
    }

}