synchronized实现共同变量访问时的并发安全

1)不安全的代码

package com.atguigu.test;

public class Test {
    public static int count = 0;

    public static void add() {
        count++;
    }

    public static void sub() {
        count--;
    }

    public static void main(String[] args) throws Exception {
        new Thread(() -> {
            for(int i = 0; i < 100000; i++){
                add();
            }
        }).start();

        new Thread(() -> {
            for(int i = 0; i < 100000; i++){
                sub();
            }
        }).start();

        Thread.sleep(2000);

        /**
         * -2879
         *  其实每次访问,发现打印的这个值都不太一样
         */
        System.out.println(count);
    }
}

2)并发安全的代码

package com.atguigu.test;

public class TestSync {
    public static int count = 0;

    public synchronized static void add() {
        count++;
    }

    public synchronized static void sub() {
        count--;
    }

    public static void main(String[] args) throws Exception {
        new Thread(() -> {
            for (int i = 0; i < 100000; i++) {
                add();
            }
        }).start();

        new Thread(() -> {
            for (int i = 0; i < 100000; i++) {
                sub();
            }
        }).start();

        Thread.sleep(2000);

        System.out.println(count); // 始终是0
    }
}

 

来源：CSDN

作者：cocos+unity+node

链接：https://blog.csdn.net/themagickeyjianan/article/details/104358783