Design a Stack using Array with certain capacity

valid stack range [0, head)


public MyStack<E> {

    private final int CAPACITY = 10;
    private int head;
    private E[] array;

    public MyStack(int capacity) {
        this.array = new E[capacity];
        this.head = 0;
    }

    public MyStack() {
        this(CAPACITY);
    }
    public boolean empty() {
        return head == 0;
    }

    public boolean push(E element) {
        if (head >= array.length) return false;
        array[head++] = element;
        return true;
    }

    public E pop() {
        if (head == 0) return null;
        return array[--head];
    }
    public E peek() {
        //if (head == 0) return null;
        //return array[head - 1];
        return (head == 0) ? null : array[head - 1];
    }
}