ArrayDeque my own Implementation in Java

ArrayDeque.java

package adt.deque;

/**
 * Implementing a Deque with a Circular Array.
 * 
 * @author Samuel T. C. Santos
 * @version 1.0
 * @param <E>
 */
public class ArrayDeque<E> implements Deque<E> {
	
	private E[] data;
	private static final int CAPACITY = 5;
	private int front = 0;
	private int back = 0;
	
	private int size = 0;
	
	/**
	 * Constructs a ArrayDeque with default capacity.
	 */
	public ArrayDeque(){
		this(CAPACITY);
	}
	
	/**
	 * Constructs a ArrayDeque with a given capacity.
	 * 
	 * @param capacity
	 */
	@SuppressWarnings("unchecked")
	public ArrayDeque(int capacity){
		if (capacity <= 0 ){
			throw new IllegalArgumentException("Invalid Capacity!");
		}
		data = (E[]) new Object[capacity];
	}
	
	@Override
	public int size() {
		return size;
	}

	@Override
	public boolean isEmpty() {
		return size == 0;
	}

	@Override
	public E first() {
		return isEmpty() ? null : data[front];
	}

	@Override
	public E last() {
		return isEmpty() ? null : data[back];
	}

	@Override
	public void addFirst(E element) throws DequeOverflowException {
		if (size == data.length)
			throw new DequeOverflowException();
		if (isEmpty()){
			data[front] = element;
		}
		else{
			front = (front - 1 + data.length)  % data.length;
			data[front] = element;
		}
		size++;
	}

	@Override
	public void addLast(E element) throws DequeOverflowException {
		if (size == data.length)
			throw new DequeOverflowException();
		
		back = back  % data.length;
		data[back] = element;
	
		size++;
	}

	@Override
	public E removeFirst() throws DequeUnderflowException {
		if (isEmpty())
			throw new DequeUnderflowException();
		
		E answer = data[front];
		front = (front + 1) % data.length;
		size--;
		
		return answer;
	}

	@Override
	public E removeLast() throws DequeUnderflowException {
		if (isEmpty())
			throw new DequeUnderflowException();
		
		E answer = data[back];
		back = (back - 1 + data.length) % data.length;
		size--;
		
		return answer;
	}
	
}

Hi! I think there is a mistake in this code. If you do:

add first -479
delete last
add last -119
delete first

You get the following result:

-479
-479

While the correct answer is:

-479
-119