【Java集合源码04】Stack源码分析

た入场券 2023-01-03 14:12 160阅读 0赞

# 简介 #

Stack是栈，先入后出，继承自Vector，所以是线程安全的。遗留类，不推荐使用，可用Deque模拟战。本质上还是用数组实现的，数组尾部就是栈顶。

Deque<Integer> stack = new LinkedList<>();
    stack.addFirst(12);
    stack.pollFirst();

![20201206215001.png][]

# 源码 #

源码比较简单

package java.util;
    
    
    public
    class Stack<E> extends Vector<E> {
        
        /**
         * Creates an empty Stack.
         */
        public Stack() {
        
        }
    
        public E push(E item) {
        
            // 添加到数组尾部
            addElement(item);
    
            return item;
        }
    
        public synchronized E pop() {
        
            E       obj;
            int     len = size();
            // 获得数组最后一个元素
            obj = peek();
            // 删除数组最后一个元素
            removeElementAt(len - 1);
    
            return obj;
        }
    
        /**
         * Looks at the object at the top of this stack without removing it
         * from the stack.
         *
         * @return  the object at the top of this stack (the last item
         *          of the <tt>Vector</tt> object).
         * @throws  EmptyStackException  if this stack is empty.
         */
        public synchronized E peek() {
        
            int     len = size();
    
            if (len == 0)
                throw new EmptyStackException();
            return elementAt(len - 1);
        }
    
        /**
         * Tests if this stack is empty.
         *
         * @return  <code>true</code> if and only if this stack contains
         *          no items; <code>false</code> otherwise.
         */
        public boolean empty() {
        
            return size() == 0;
        }
    
    	// 返回o所在的索引位置
        public synchronized int search(Object o) {
        
            int i = lastIndexOf(o);
    
            if (i >= 0) {
        
                return size() - i;
            }
            return -1;
        }
    
        /** use serialVersionUID from JDK 1.0.2 for interoperability */
        private static final long serialVersionUID = 1224463164541339165L;
    }

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[20201206215001.png]: /images/20221119/bd948decac4b4ebd8ea7fd3aa7f5c12c.png
[gzh.jpg]: /images/20221119/4e573e4c1ff04c329afdafce50f46682.png