线程安全性-原子性-synchronized_synchronized原子性-优快云博客

本文链接：https://blog.youkuaiyun.com/zhongzifu4948/article/details/79700080

修饰代码块：大括号括起来的代码，作用于调用的对象

修饰方法：整个方法，作用于调用的对象

修饰静态方法：作用于所有对象

修饰类：括号括起来的部分，作用于所有对象

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

@Slf4j
public class SynchronizedExample1 {

    // 修饰一个代码块
    public void test1(int j) {
        synchronized (this) {
            for (int i = 0; i < 10; i++) {
                log.info("test1 {} - {}", j, i);
            }
        }
    }

    // 修饰一个方法
    public synchronized void test2(int j) {
        for (int i = 0; i < 10; i++) {
            log.info("test2 {} - {}", j, i);
        }
    }

    public static void main(String[] args) {
        SynchronizedExample1 example1 = new SynchronizedExample1();
        SynchronizedExample1 example2 = new SynchronizedExample1();
        ExecutorService executorService = Executors.newCachedThreadPool();
        executorService.execute(() -> {
            example1.test1(1);
        });
        executorService.execute(() -> {
            example1.test1(2);
        });
    }
}

example1.test1(1);example1.test1(2);

或者example1.test2(1);example1.test2(2);

输出

16:45:36.274 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 1 - 0
16:45:36.277 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 1 - 1
16:45:36.277 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 1 - 2
16:45:36.277 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 1 - 3
16:45:36.278 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 1 - 4
16:45:36.278 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 1 - 5
16:45:36.278 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 1 - 6
16:45:36.278 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 1 - 7
16:45:36.278 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 1 - 8
16:45:36.278 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 1 - 9
16:45:36.278 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 2 - 0
16:45:36.278 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 2 - 1
16:45:36.278 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 2 - 2
16:45:36.278 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 2 - 3
16:45:36.278 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 2 - 4
16:45:36.278 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 2 - 5
16:45:36.278 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 2 - 6
16:45:36.278 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 2 - 7
16:45:36.278 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 2 - 8
16:45:36.278 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample1 - test1 2 - 9

example1.test1(1);example2.test1(2);

或者example1.test2(1);example2.test2(2);

输出

17:26:48.472 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 0
17:26:48.475 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 1
17:26:48.475 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 2
17:26:48.476 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 3
17:26:48.476 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 4
17:26:48.476 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 5
17:26:48.476 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 6
17:26:48.476 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 7
17:26:48.476 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 8
17:26:48.476 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 9
17:26:48.476 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 0
17:26:48.476 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 1
17:26:48.476 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 2
17:26:48.476 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 3
17:26:48.476 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 4
17:26:48.476 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 5
17:26:48.476 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 6
17:26:48.476 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 7
17:26:48.476 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 8
17:26:48.476 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 9

很明显证明作用于对象

package com.mmall.concurrency.example.sync;

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

@Slf4j
public class SynchronizedExample2 {

    // 修饰一个类
    public static void test1(int j) {
        synchronized (SynchronizedExample2.class) {
            for (int i = 0; i < 10; i++) {
                log.info("test1 {} - {}", j, i);
            }
        }
    }

    // 修饰一个静态方法
    public static synchronized void test2(int j) {
        for (int i = 0; i < 10; i++) {
            log.info("test2 {} - {}", j, i);
        }
    }

    public static void main(String[] args) {
        SynchronizedExample2 example1 = new SynchronizedExample2();
        SynchronizedExample2 example2 = new SynchronizedExample2();
        ExecutorService executorService = Executors.newCachedThreadPool();
        executorService.execute(() -> {
            example1.test1(1);
        });
        executorService.execute(() -> {
            example2.test1(2);
        });
    }
}

example1.test1(1);example2.test1(2)

或example1.test2(1);example2.test2(2)

17:28:35.181 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 0
17:28:35.186 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 1
17:28:35.186 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 2
17:28:35.186 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 3
17:28:35.186 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 4
17:28:35.186 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 5
17:28:35.186 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 6
17:28:35.186 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 7
17:28:35.186 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 8
17:28:35.186 [pool-1-thread-1] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 1 - 9
17:28:35.186 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 0
17:28:35.186 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 1
17:28:35.186 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 2
17:28:35.186 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 3
17:28:35.186 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 4
17:28:35.186 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 5
17:28:35.186 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 6
17:28:35.186 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 7
17:28:35.186 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 8
17:28:35.186 [pool-1-thread-2] INFO com.mmall.concurrency.example.sync.SynchronizedExample2 - test1 2 - 9

明显左右于类上，只能一个对象调用方法