Java 慎用方法级别的synchronized关键字

转自： http://www.jiacheo.org/blog/317

为什么要这么说呢， 因为笔者被这个坑过（其实是自己坑自己）╮(╯_╰)╭

synchronized void  a(){
  countDownLatch = new CountDownLatch(1);
  // do someing
  countDownLatch.await();
}

synchronized void b(){
     countDownLatch.countDown();
}

byte[]  mutex = new byte[0];

void a1(){
     synchronized(mutex){
          //dosomething
     }
}

void b1(){

     synchronized(mutex){
          // dosomething
     }

}

public class MultiThreadSync {

    public synchronized void m1() throws InterruptedException{
         System. out.println("m1 call" );
         Thread. sleep(2000);
         System. out.println("m1 call done" );
    }

    public void m2() throws InterruptedException{
          synchronized (this ) {
             System. out.println("m2 call" );
             Thread. sleep(2000);
             System. out.println("m2 call done" );
         }
    }

    public static void main(String[] args) {
          final MultiThreadSync thisObj  = new MultiThreadSync();

         Thread t1 = new Thread(){
              @Override
              public void run() {
                  try {
                      thisObj.m1();
                 } catch (InterruptedException e) {
                      e.printStackTrace();
                 }
             }
         };

         Thread t2 = new Thread(){
              @Override
              public void run() {
                  try {
                      thisObj.m2();
                 } catch (InterruptedException e) {
                      e.printStackTrace();
                 }
             }
         };

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

    }

}

                                        void method(){
void synchronized method(){                 synchronized(this){
      // biz code                               // biz code
}                             ------>>>      }
                                        }