Interthread Communication

Java includes an elegant Interprocess communication mechanism via the wait(), notify() and notifyAll() methods.These methods are implemented as final method in object, so all classes have them. all three methods can be called only from within a synchronized context. Although conceptually advanced from a computer science perspective, the rules for using these methods are actually quite simple:
wait(): Tells the calling thread to given up the monitor and go to sleep until some other thread enters the same monitor and calls notify() or notifyAll().
notify(): wakes up a thread that called wait() on the same object.
notifyAll(): wakes up a thread that called wait() on the same object. One of the threads will be granted access.

These methods are declared within Object, as shown here:
final void wait()throws InterruptedException final void notify() final void notifyAll()
The proper way to write this program in java is to use wait() and notify() to signal in both directions, shown here:
//A correct implemenetation of a producer and consumet. class Q{ int n; boolean valueSet=false; synchronized int get(){ while(!valueSet) try{ wait(); }catch(InterruptedException e){ System.out.println("InterruptedException caught"); } System.out.println("Got: " +n); valueSet=false; notify(); return n; } synchronized void put(int n){ while(valueSet) try{ wait(); }catch(InterruptedException e){ System.out.println("InterruptedException caught"); } this.n=n; valueSet=true; System.out.println("PUT: " +n); notify(); } } class producer implements Runnable{ Q q; producer(Q q){ this.q=q; new Thread(this, "Producer").start(); } public void run(){ int i=0; while(i<10){ q.put(i++); } } } class consumer implements Runnable{ Q q; consumer(Q q){ this.q=q; new Thread(this, "consumer").start(); } public void run(){ while(true){ q.get(); } } } class PCFixed{ public static void main(String []arg){ Q q=new Q(); new producer(q); new consumer(q); System.out.println("Please control-c to stop"); }}
Output: