JAVA静态方法同步

public class StaticSynTest extends Thread {

StaticMothod sm;

public StaticSynTest(StaticMothod sm){

this.sm = sm;

}

public static void main(String[] args) {

StaticMothod sm1 = new StaticMothod();

StaticSynTest sst1 = new StaticSynTest(sm1);

StaticSynTest sst2 = new StaticSynTest(sm1);

StaticSynTest sst3 = new StaticSynTest(sm1);

sst1.setName("sst1");

sst2.setName("sst2");

sst3.setName("sst3");

sst1.start();

sst2.start();

sst3.start();

}

public void run(){

this.sm.b(Thread.currentThread().getName());

this.sm.b1(Thread.currentThread().getName());

StaticMothod.a(Thread.currentThread().getName());

StaticMothod.a1(Thread.currentThread().getName());

}

}

class StaticMothod{

public synchronized static void a(String name){

System.out.println(name+":a in");

try{

Thread.sleep(2000);

System.out.println("");

}

catch(InterruptedException e){

}

System.out.println(name+":a out");

}

public synchronized static void a1(String name){

System.out.println(name+":a1 in");

try{

Thread.sleep(2000);

System.out.println("");

}

catch(InterruptedException e){

}

System.out.println(name+":a1 out");

}

public synchronized void b(String name){

System.out.println(name+":b in");

try{

Thread.sleep(2000);

System.out.println("");

}

catch(InterruptedException e){

}

System.out.println(name+":b out");

}

public synchronized void b1(String name){

System.out.println(name+":b1 in");

try{

Thread.sleep(2000);

System.out.println("");

}

catch(InterruptedException e){

}

System.out.println(name+":b1 out");

}

}
输出结果为：
sst1:b in

sst1:b out

sst2:b in

sst2:b out

sst3:b in

sst3:b out

sst1:b1 in

sst1:b1 out

sst1:a in

sst2:b1 in

sst1:a out

sst1:a1 in

sst2:b1 out

sst3:b1 in

sst3:b1 out

sst1:a1 out

sst2:a in

sst2:a out

sst3:a in

sst3:a out

sst2:a1 in

sst2:a1 out

sst3:a1 in

sst3:a1 out

结论：
1、当前线程调用类的同步静态方法时，其它线程可以进入该类实例的其它非静态方法，不能进入类的其它静态方法。
2、同理，当前进入同步的实例方法时，其它线程可以进入该类的静态方法，但是不能进入该类的其它非静态方法。
原因：静态方法同步是获取StaticSynTest.class锁，而实例方法获取的是该“实例对象”的锁，它们互不干涉。
转载自 http://hi.baidu.com/knoic/blog/item/8061202c1e0c93f08b1399c6.html