public class ArrayPile<E> implements Pile<E>{

    int size = 16;
    int currentElement = 0;

    E[] table;

    public ArrayPile() {
        table = (E[])new Object[size];
    };

    private void resizeStack() {
        size *= 2;
        E[] newTable = (E[])new Object[size];

        for (int i = 0; i < table.length; i++) {
            newTable[i] = table[i];
        }

        table = newTable;
    }

    @Override
    public E getFirst() {
        if (currentElement == 0) {
            return null;
        } else {
            return table[currentElement-1];
        }
    }

    @Override
    public E pollFirst() {
        if (currentElement == 0) {
            return null;
        } else {
            E e = table[currentElement-1];
            currentElement--;
            return e;
        }
    }

    @Override
    public void addFirst(E e) {
        if (currentElement >= table.length) resizeStack();
        table[currentElement] = e;
        currentElement++;
    }

    @Override
    public int size() {
        return currentElement;
    }
    
}