如何在main方法中调用wait（）方法？ 如果我使用它，它将给出java.lang.IllegalMonitorStateException

Question

I get an error :

    package main_test;
    public class Main {
    public static void main(String[] args) throws InterruptedException
    {
        Main m = new Main();
        System.out.println("Main Started");
            m.wait();
        System.out.println("Main Terminated");  
    }
}

Answer 1

You have to acquire the lock first, before you can call wait. Try something like this:

  public static void main(String[] args) throws InterruptedException {
    Main m = new Main();
    System.out.println("Main Started");
    synchronized (m) {
      m.wait();
    }
    System.out.println("Main Terminated");
  }

But now the program will not terminate - obviously. Some other thread needs to call notify() on the object you called wait() . (This is why its a bad idea to use a local variable but this is just an example so...)

See the java tutorial for more information.

Answer 2

public static void main(String[] args) throws InterruptedException {

        Main m = new Main();
        System.out.println("Main Started");
        synchronized (m) {
            m.wait();
        }

        System.out.println("Main Terminated");
    }

Program wont terminate!!

Answer 3

You have to explicitly acquire monitor by making particular block or method synchronized. wait() releases lock held by executing thread and notify() informs other thread for execution.

Example:

Object lock= new Object();
synchronized(lock){
// write your code here. You may use wait() or notify() as per your requirement.
    wait(1000);
    notify();
}

Alternatively you may use synchronized method:

public synchronized void putMessage(){
// write your code
wait(1000);
notify();
// write your code
}