Java implements a very efficient interprocess communication which reduces the CPU’s idle time to a very great extent. It is been implemented through wait ( ), notify ( ) and notifyAll ( ) methods. Since these methods are implemented as final methods they are present in all the classes.

The basic functionality of each one of them is as under:

■ wait( ) acts as a intimation to the calling thread to give up the monitor and go to sleep until some other thread enters the same monitor and calls notify( ).

■ notify( ) is used as intimator to wake up the first thread that called wait( ) on the same object.

■ notifyAll( ) as the term states wakes up all the threads that called wait( ) on the same object. The highest priority thread will run first.

public class WaitNotifyAllExample {
 
public static void main(String[] args) {
 
try {
Object o = new Object();
Thread thread1 = new Thread(new MyOwnRunnable("A", o));
Thread thread2 = new Thread(new MyOwnRunnable("B", o));
Thread thread3 = new Thread(new MyOwnRunnable("C", o));
 
// synchronized keyword acquires lock on the object.
synchronized (o) {
thread1.start();
// wait till the first thread completes execution.
// thread should acquire the lock on the object
// before calling wait method on it. Otherwise it will
// throw java.lang.IllegalMonitorStateException 
o.wait();
thread2.start();
// wait till the second thread completes execution
o.wait();
thread3.start();
}
 
}
catch (InterruptedException e) {
e.printStackTrace();
}
 
}
}
 
class MyOwnRunnable implements Runnable {
 
private String threadName;
 
private Object o;
 
public MyOwnRunnable(String name, Object o) {
threadName = name;
this.o = o;
}
 
public void run() {
 
 
synchronized (o) {
for (int i = 0; i < 1000; i++) {
System.out.println("Thread " + threadName + " Count : " + i);
}
// notify all threads waiting for the object o.
// thread should acquire the lock on the object
// before calling notify or notifyAll method on it. 
// Otherwise it will throw java.lang.IllegalMonitorStateException 
o.notifyAll();
}
}
}