synchronized三种使用方式，及锁的类型验证

Synchronized常用三种使用方式

1、修饰普通方法：锁对象即为当前对象

2、修饰静态方法：锁对象为当前Class对象

3、修饰代码块：锁对象为synchronized紧接着的小括号内的对象

一、验证修饰普通方法时锁对象

package com.demo;

public class ThreadTest {

    public static void main(String[] args) {
        Thread t1 = new MyThread1();
        Thread t2 = new MyThread2(t1);

        t1.start();// 默认priority=5
        t2.start();

        t2.setPriority(9);

        System.out.println("线程1：" + t1.getState());
        System.out.println("线程2：" + t2.getState());
    }

}

class MyThread1 extends Thread {

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

    public synchronized void dosome() {
        System.out.println("mythread1");
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("sleep end");
    }
}

class MyThread2 extends Thread {
    private Object lock;

    public MyThread2(Object lock) {
        this.lock = lock;
    }

    @Override
    public void run() {
        synchronized (lock) {
            System.out.println("mythread2");
        }
    }

}

现象：先逐行输出mythread1，线程1：RUNNABLE，线程2：BLOCKED，之后暂停五分钟，逐行输出sleep end，mythread2

分析：线程2与线程1拥有相同的锁，线程1优先级高于线程2，线程1优先执行，获取到锁，执行sleep，未释放锁，线程2未获取到锁，处于阻塞状态，线程1sleep结束，输出sleep end，并释放锁，线程2获取到锁，执行输出mythread2

结论：当synchronized修饰普通方法时，锁对象即为当前对象

二、验证修饰静态方法时锁对象

对上述代码稍作修改，在dosome方法上添加static关键字，main方法中，线程2对象初始化时，传入MyThread1.class

现象：与上述现象一致

分析：同上

结论：当synchronized修饰静态方法时，锁对象为当前Class对象

三、验证修饰代码块时锁对象

package com.demo;

public class ThreadTest {

    public static void main(String[] args) {
        Object o = new Object();

        Thread t1 = new MyThread1(o);
        Thread t2 = new MyThread2(o);

        t1.start();
        t2.start();

        t2.setPriority(9);
        System.out.println("线程1：" + t1.getState());
        System.out.println("线程2：" + t2.getState());

    }

}

class MyThread1 extends Thread {
    private Object lock;

    public MyThread1(Object lock) {
        this.lock = lock;
    }

    @Override
    public void run() {

        synchronized (lock) {
            System.out.println("mythread1");
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("sleep end");
        }
    }

}

class MyThread2 extends Thread {
    private Object lock;

    public MyThread2(Object lock) {
        this.lock = lock;
    }

    @Override
    public void run() {
        synchronized (lock) {
            System.out.println("mythread2");
        }
    }

}

现象：同上

分析：同上

结论：当使用synchronized修改代码块时，其后小括号中的对象即为对象锁。