Differnce between addfirst and offerFirst methods in ArrayDeque

Question

Have tried out a sample program to understand the difference between addFirst and offerFirst methods in ArrayDeque of Java 6. But they

Answer 1

the source code of offerFirst :

 public boolean offerFirst(E e) {
        addFirst(e);
        return true;
    }

And addFirst

 public void addFirst(E e) {
        if (e == null)
            throw new NullPointerException();
        elements[head = (head - 1) & (elements.length - 1)] = e;
        if (head == tail)
            doubleCapacity();
    }

offerFirst returns true, thats the only difference ...