this锁（对象锁）

• 同步方法默认使用的this锁

public class SynchronizedThis {

    public static void main(String[] args) {
        ThisLock thisLock = new ThisLock();
        new Thread("T1"){
            @Override
            public void run() {
                thisLock.m1();
            }
        }.start();
        new Thread("T2"){
            @Override
            public void run() {
                thisLock.m2();
            }
        }.start();
    }
}

class ThisLock{


    public synchronized void  m1(){
        try {
            System.out.println(Thread.currentThread().getName());
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public synchronized void  m2(){
        try {
            System.out.println(Thread.currentThread().getName());
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

• 执行后，可以观察到两个同步方法，在多个线程并发访问一个对象不同方法的时候，会被锁住

Class锁

• 当定义的同步方法是静态方法时，此时加的锁是Class锁

public class SynchronizedStatic {

    public static synchronized void  m1(){
        try {
            System.out.println(Thread.currentThread().getName());
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static synchronized void  m2(){
        try {
            System.out.println(Thread.currentThread().getName());
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}