Graphical code analysis of Java collection Stack

public  class Stack<E> extends Vector<E> {

    public Stack() {//创建空栈
    }

    public E push(E item) {//入栈
        addElement(item);
        return item;
    }
    //出栈
    public synchronized E pop() {
        E       obj;
        int     len = size();
        obj = peek();
        removeElementAt(len - 1);
        return obj;
    }
    //返回栈顶元素，但并不出栈
    public synchronized E peek() {
        int     len = size();

        if (len == 0)
            throw new EmptyStackException();
        return elementAt(len - 1);
    }
    //判断栈是否为空
    public boolean empty() {
        return size() == 0;
    }
    //查找元素并返回栈深
    public synchronized int search(Object o) {
        int i = lastIndexOf(o);

        if (i >= 0) {
            return size() - i;
        }
        return -1;
    }

    //序列版本号
    private static final long serialVersionUID = 1224463164541339165L;
}