public void push(int item) {
StackNode node = new StackNode(item);
if (top == null) {
top = node;
return;
}
node.next = top;
top = node;
}
/** @param the element to push */
public void push(E e) {
StackNode<E> node = new StackNode(e);
node.next = top;
top = node;
}