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();      }  }