public Item pop() throws EmptyStackException {
if (size == 0) throw new EmptyStackException();
size--;
Item item = stack[size];
stack[size] = null; // avoid loitering!
if (size <= stack.length / 4) resize(stack.length / 2);
return item;
}
public Item pop() {
if (isEmpty()) throw new NoSuchElementException();
Item item = a[--N];
a[N] = null;
if (N > 0 && N <= a.length / 4) resize(a.length / 2);
return item;
}
public void push(Item item) {
if (size == stack.length) resize(2 * stack.length);
stack[size] = item;
size++;
}
public void push(Item item) {
if (N >= a.length) resize(2 * a.length);
a[N++] = item;
}