2つのスレッドの交互実行

public class TwoThreadLock {
    private static Object lock = new Object();  
    private static boolean flag = false;  
      
    public static void main(String[] args) {  
          
        Thread a = new Thread(){  
            public void run()  
            {  
                while(true)  
                {  
                    synchronized(lock)  
                    {  
                        System.out.println("Thread1");  
                          
                        if(flag)  
                        {  
                            flag = false;  
                            lock.notify();  
                            try {  
                                lock.wait();  
                            } catch (InterruptedException e) {  
                                // TODO Auto-generated catch block  
                                e.printStackTrace();  
                            }  
                        }  
                    }  
                }  
            }  
        };  
          
        Thread b = new Thread(){  
            public void run()  
            {  
                while(true)  
                {  
                    synchronized(lock)  
                    {  
                        System.out.println("Thread2");  
                          
                        if(!flag)  
                        {  
                            flag =true;  
                            try {  
                                lock.wait(); 
                                lock.notify();  
                                 
                            } catch (Exception e) {  
                                // TODO: handle exception  
                                e.printStackTrace();  
                            }  
                        }  
                    }      
                }  
            }  
        };  
          
        a.start();  
        b.start();  
    }  
}