多线程同步调试1

主类

public class Main {
  
 public static void main(String args[]){
  Thread a = new Thread(new TreadAdd());
  Thread b = new Thread(new TreadAdd());
  Thread c = new Thread(new TreadAdd());
  a.start();
  b.start();
  c.start();
 }
}

线程类

public class TreadAdd implements Runnable{
 private  int  total  = 100;
  Object obj = new Object();
 @Override
 public  void  run() {
     while(true){
      synchronized(obj){
       if(Variable.aa>0){
        try {
      Thread.sleep(100);
     } catch (InterruptedException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
     }
     Variable.aa--;
        System.out.println(Thread.currentThread().getName()+"the total is"+Variable.aa);
       }
       }
     }
 }
  
}

运行觉果如下

Thread-0the total is31
Thread-1the total is30
Thread-2the total is29
Thread-0the total is28
Thread-1the total is27
Thread-0the total is26
Thread-2the total is25
Thread-0the total is24
Thread-2the total is23
Thread-1the total is22
Thread-0the total is21
Thread-2the total is20
Thread-1the total is19
Thread-0the total is18
Thread-2the total is17
Thread-1the total is16
Thread-0the total is15
Thread-2the total is14
Thread-1the total is13
Thread-0the total is12
Thread-2the total is11
Thread-1the total is10
Thread-2the total is9
Thread-0the total is8
Thread-1the total is7
Thread-2the total is6
Thread-0the total is5
Thread-1the total is4
Thread-2the total is3
Thread-0the total is2
Thread-1the total is1
Thread-0the total is0
Thread-2the total is-1
Thread-1the total is-2

明明加了synchronized同步，为什么还会有-1和-2这种情况呢

原因是主类中创建了三次线程类将主类改为

public class Main {
  
 public static void main(String args[]){
  TreadAdd  t = new TreadAdd();
  Thread a = new Thread(t);
  Thread b = new Thread(t);
  Thread c = new Thread(t);
  a.start();
  b.start();
  c.start();
 }
}

就避免了这种情况。