实现

Stack 是基于 Vector 实现的，线程安全

push

添加元素到末尾

  1. public E push(E item) {
  2.     addElement(item);
  3.     return item;
  4. }

pop、peek

直接从末尾移除元素

  1. public synchronized E pop() {
  2.     E       obj;
  3.     int     len = size();
  4.     obj = peek();
  5.     removeElementAt(len - 1);
  6.     return obj;
  7. }
  9. public synchronized E peek() {
  10.     int     len = size();
  11.     if (len == 0)
  12.         throw new EmptyStackException();
  13.     return elementAt(len - 1);
  14. }