Java Improvement (Sanyi)-----Stack

In Java, the Stack class represents a last-in-first-out (LIFO) object stack. The stack is a very common data structure that uses a typical first-in-last-out operation. Each stack contains a stack top. Each time the stack is popped, the data on the top of the stack is taken out, as follows:

Stack extends Vector with five operations, allowing vectors to be treated as stacks. The five operations are as follows:

public class Stack<E> extends Vector<E>

/**
     * 构造函数
     */
    public Stack() {
    }

    /**
     *  push函数：将元素存入栈顶
     */
    public E push(E item) {
        // 将元素存入栈顶。
        // addElement()的实现在Vector.java中
        addElement(item);

        return item;
    }

    /**
     * pop函数：返回栈顶元素，并将其从栈中删除
     */
    public synchronized E pop() {
        E    obj;
        int    len = size();

        obj = peek();
        // 删除栈顶元素，removeElementAt()的实现在Vector.java中
        removeElementAt(len - 1);

        return obj;
    }

    /**
     * peek函数：返回栈顶元素，不执行删除操作
     */
    public synchronized E peek() {
        int    len = size();

        if (len == 0)
            throw new EmptyStackException();
        // 返回栈顶元素，elementAt()具体实现在Vector.java中
        return elementAt(len - 1);
    }

    /**
     * 栈是否为空
     */
    public boolean empty() {
        return size() == 0;
    }

    /**
     *  查找“元素o”在栈中的位置：由栈底向栈顶方向数
     */
    public synchronized int search(Object o) {
        // 获取元素索引，elementAt()具体实现在Vector.java中
        int i = lastIndexOf(o);

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

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