synchronized学习笔记（一）：object锁与class锁

synchronized作为java并发编程最重要的知识点之一，用法大致可以分为两点，对象（object）锁与类（class）锁，各自又可以再细分为代码块锁与方法锁。本文主要对这四种情况的基本用法进行整理。

对象-代码块锁

public class SynchronizedObjectCodeBlock implements Runnable {
    static SynchronizedObjectCodeBlock instance = new SynchronizedObjectCodeBlock();

    public static void main(String[] args) {
        Thread t1 = new Thread(instance);
        Thread t2 = new Thread(instance);
        t1.start();
        t2.start();
        while(t1.isAlive() || t2.isAlive()){
        }
        System.out.println("finished");
    }

    @Override
    public void run() {
        synchronized (this) {
            System.out.println("object的代码块锁，线程：" + Thread.currentThread().getName());
            try {
                Thread.sleep(3000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + "运行结束。");
        }
    }
}

对象-方法锁

public class SynchronzizedObjectMethod implements Runnable{
    static SynchronzizedObjectMethod instance = new SynchronzizedObjectMethod();

    public static void main(String[] args){
        Thread t1 = new Thread(instance);
        Thread t2 = new Thread(instance);
        t1.start();
        t2.start();
        while(t1.isAlive() || t2.isAlive()){
        }
        System.out.println("finished");
    }

    @Override
    public void run() {
        method();
    }

    public synchronized void method(){
        System.out.println("对象锁的方法锁，线程："+Thread.currentThread().getName());
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(Thread.currentThread().getName() + "运行结束");
    }
}

类-代码块

public class SynchronizedClassClass implements Runnable{
   static SynchronizedClassClass instance1 = new SynchronizedClassClass();
   static SynchronizedClassClass instance2 = new SynchronizedClassClass();

   public static void main(String[] args){
       Thread t1 = new Thread(instance1);
       Thread t2 = new Thread(instance2);
       t1.start();
       t2.start();
       while(t1.isAlive() || t2.isAlive()){}
       System.out.println("finished");
   }

   public void method(){
       synchronized (SynchronizedClassClass.class){
           System.out.println("类锁的：*.class形式。线程：" + Thread.currentThread().getName());
           try {
               Thread.sleep(3000);
           } catch (InterruptedException e) {
               e.printStackTrace();
           }
           System.out.println(Thread.currentThread().getName() + "运行结束");
       }
   }

   @Override
   public void run() {
       method();
   }
}

类-方法锁：

public class SychronizedClassStatic implements Runnable{
    static SychronizedClassStatic instance1 = new SychronizedClassStatic();
    static SychronizedClassStatic instance2 = new SychronizedClassStatic();

    public static void main(String[] args){
        Thread t1 = new Thread(instance1);
        Thread t2 = new Thread(instance2);
        t1.start();
        t2.start();
        while(t1.isAlive() || t2.isAlive()){}
        System.out.println("finished");
    }

    public static synchronized void method(){
        System.out.println("类锁的static方法形式。线程："+ Thread.currentThread().getName());
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(Thread.currentThread().getName()+"运行结束");
    }

    @Override
    public void run() {
        method();
    }
}

本文参考慕课网课程《Java高并发之魂：synchronized深度解析》
https://www.imooc.com/learn/1086