// Implementation of a circular queue
// Uses an ArrayList since we can't create an
//  array of generic type.  The size of the ArrayList doesn't change
//
// d. frey  july 2011

import java.util.*;

public class CircularQueue<T>
{
    private int head, tail, size, nrElements;
    private ArrayList<T> elements;

    public CircularQueue( int maxSize )
    {
	// add(null) initializes contents of elements
	// so that set( ) may be used to enqueue
	elements = new ArrayList<T> (maxSize);
	for( int i = 0; i < maxSize; i++)
	    elements.add( null );

	size = maxSize;
	makeEmpty( );
    }

    // make the queue logically empty
    public void makeEmpty( )
    {
	    
	head = 0;
	tail = -1;
	nrElements = 0;
    }

    public boolean isEmpty( )
    {
	return nrElements == 0;
    }

    public boolean isFull( )
    {
	return nrElements == size;
    }

    public boolean enqueue( T x )
    {
	if (isFull()) return false;

	tail = ++tail % size;
	elements.set( tail, x);
	++nrElements;
	return true;
    }

    public T dequeue( )
    {
	if (isEmpty()) return null;

	T item = elements.get( head );
	head = ++head % size;
	--nrElements;
	return item;
    }

    public void print( )
    {
	System.out.println( "size = " + size);
	System.out.println( "nrElements = " + nrElements);
	System.out.println( "head = " + head);
	System.out.println( "tail = " + tail);
	for( int i = 0; i < size; i++)
	    System.out.println( elements.get(i));
    }



    public static void main( String args[])
    {
	CircularQueue<Integer> q = new CircularQueue<Integer>( 6 );
	q.print( );
	System.out.println("in 11"); q.enqueue(11);
	q.print( );
	System.out.println("in 12"); q.enqueue(12);
	q.print( );
	System.out.println("in 13"); 	q.enqueue(13);
	q.print( );
	System.out.println("in 14"); 	q.enqueue(14);
	q.print( );

	Integer x;
	System.out.println("dq 11"); 	x = q.dequeue();
	q.print( );
	System.out.println("dq 12"); 	x = q.dequeue();
	q.print( );
	System.out.println("in 15"); 	q.enqueue( 15);
	q.print( );
	System.out.println("in 16"); 	q.enqueue(16);
	q.print();
    }
};