wait

Object wait methods has three variance, one which waits indefinitely for any other thread to call notify or notifyAll method on the object to wake up the current thread.

notify

notify method wakes up only one thread waiting on the object and that thread starts execution.

notifyAll

notifyAll method wakes up all the threads waiting on the object, although which one will process first depends on the OS implementation.

https://raw.githubusercontent.com/vsaravanan/java22/master/src/main/java/com/saravanjs/java22/console/multithreading/WaitNotifyTest.java

Java Thread wait, notify and notifyAll Example | DigitalOcean

class Message {
private String msg;

public Message(String str){
this.msg=str;
    }

public String getMsg() {
return msg;
    }

public void setMsg(String str) {
this.msg=str;
    }

}

class Waiter implements Runnable{

private Message msg;

public Waiter(Message m){
this.msg=m;
    }

@Override
public void run() {
String name = Thread.currentThread().getName();
synchronized (msg) {
try{
System.out.println(name+" waiting to get notified at time:"+System.currentTimeMillis());
msg.wait();
            }catch(InterruptedException e){
e.printStackTrace();
            }
System.out.println(name+" waiter thread got notified at time:"+System.currentTimeMillis());
//process the message now
System.out.println(name+" processed: "+msg.getMsg());
        }
    }

}

class Notifier implements Runnable {

private Message msg;

public Notifier(Message msg) {
this.msg = msg;
    }

@Override
public void run() {
String name = Thread.currentThread().getName();
System.out.println(name+" started");
try {
Thread.sleep(1000);
synchronized (msg) {
msg.setMsg(name+" Notifier work done");
msg.notify();
//                msg.notifyAll();
}
        } catch (InterruptedException e) {
e.printStackTrace();
        }

    }

}

public class WaitNotifyTest {

public static void main(String[] args) {
Message msg = new Message("process it");
Waiter waiter = new Waiter(msg);
new Thread(waiter,"waiter").start();

Waiter waiter1 = new Waiter(msg);
new Thread(waiter1, "waiter1").start();

Notifier notifier = new Notifier(msg);
new Thread(notifier, "notifier").start();
System.out.println("All the threads are started");
    }

}

for msg.notify();

All the threads are started

notifier started

waiter waiting to get notified at time:1718699314333

waiter1 waiting to get notified at time:1718699314342

waiter waiter thread got notified at time:1718699315335

waiter processed: notifier Notifier work done

for msg.notifyAll();

All the threads are started

notifier started

waiter waiting to get notified at time:1718699488848

waiter1 waiting to get notified at time:1718699488860

waiter waiter thread got notified at time:1718699489854

waiter processed: notifier Notifier work done

waiter1 waiter thread got notified at time:1718699489858

waiter1 processed: notifier Notifier work done