cis551HW6QueueClass (Java)

/**
 *  Queue<E> - circular array implementation of generic Queue<E> class;
 *             max #elements storeable is 1 less than the size of array,
 *             so we can distinguish between full and empty conditions.
 *             
 * @author christopherduarte
 * @reference robertirwin
 * @course cis551
 * @assignment Lab15
 *
 * @param <E>
 */

import java.util.Arrays;
import java.util.NoSuchElementException;

@SuppressWarnings("unchecked")  // prevents warnings for casts in peek/pop methods 

public class Queue<E> {
	private int front;  // one index counter-clockwise of first queue element
	private int rear;   // index of last queue element
	private Object[] ra;

	public Queue() {
		this.ra = new Object[10+1]; 
		this.front = 0;
		this.rear = 0;
	}

	public Queue(int initialCapacity) throws IllegalArgumentException {
		if ( initialCapacity < 1 )
			throw new IllegalArgumentException();
		// the +1 below makes up for not using one element of the object array
		this.ra = new Object[initialCapacity+1];   
		this.front = 0;
		this.rear = 0;
	}

	public void clear() {
		this.front = 0;
		this.rear = 0;
	}

	public boolean isEmpty() {
		return this.front == this.rear;
	}

	public boolean add(E e) {
		this.rear = (this.rear+1) % this.ra.length;
		if ( this.rear == this.front ) {
			Object[] tmp = Arrays.copyOf(ra, 2*this.ra.length);
			tmp[this.rear] = e;
			this.ra = tmp;
		} else {
		this.ra[this.rear] = e;}
		return true;
	}
	
	public boolean offer(E e) {
		this.rear = (this.rear+1) % this.ra.length;
		if ( this.rear == this.front )
			return false;
		this.ra[this.rear] = e;
		return true;
	}

	public E element() {
		if ( this.isEmpty() )
			throw new NoSuchElementException("tried to retrieve element from an empty queue");
		return (E)this.ra[(this.front+1) % this.ra.length];
	}

	public E peek() {
		if ( this.isEmpty() )
			return null;
		return (E)this.ra[(this.front+1) % this.ra.length];
	}

	public E peekLast() {
		if ( this.isEmpty() )
			return null;
		return (E)this.ra[this.rear];
	}

	public E remove() {
		if ( this.isEmpty() )
			throw new NoSuchElementException("tried to remove element from an empty queue");
		return (E)this.ra[this.front = (this.front+1) % this.ra.length];
	}

	public E poll() {
		if ( this.isEmpty() )
			return null;
		return (E)this.ra[this.front = (this.front+1) % this.ra.length];
	}
	
	public int size() {
		int d = this.rear - this.front;
		return d >= 0 ? d
				      : this.ra.length - d;
	}
	
	public String toString() {
		String s = "";
		for ( int i = (this.front + 1) % this.ra.length;  i != this.rear;  i = (i+1) % this.ra.length )
			s += String.format("%s%n", ((E)this.ra[i]).toString());
		s += String.format("%s%n", ((E)this.ra[this.rear]).toString());		
		return s;
	}
}