Java多线程服务器notify（）IllegalMonitorStateException

Question

I have this code

    if( id == 0 ||(id % 2) != 0){
        System.out.println("test");
        synchronized(lock) {
            try {
                out1.println("Wait for another player...");
                lock.wait();
                System.out.println("lock");
          } catch (InterruptedException e) {
            e.printStackTrace();
            }
   some code here

}else{
        System.out.println("tes1t");
        player p2 = new player(id,socket);
        Players.add(p2);
        id++;
        lock.notify();  
    }

The first time i run the client, the first block of code gets executed and it waits() until one more client gets connected. When i run the second client, and i try to notify the first block of code, it shows to me this error:

Exception in thread "NewPlayer1" java.lang.IllegalMonitorStateException
at java.lang.Object.notifyAll(Native Method)
at tictactoe.ServerClass.run(ServerClass.java:129)

Answer 1

You have to call notify in synchrnonized block

synchronized(lock) {
    player p2 = new player(id,socket);
    Players.add(p2);
    id++;
    lock.notify();  
}