inter thread communication in java

That depends on the nature of the communication.

• Is it duplex (ie A talks to B and B talks to A)?
• Is it communication of data or communication of completion?

and so on.

The simplest and most advisable form of inter-thread communication is simply to wait for the completion of other threads. That's most easily done by using Future:

ExecutorService exec = Executors.newFixedThreadPool(50);
final Future f = exec.submit(task1);
exec.submit(new Runnable() {
    @Override
    public void run() {
        f.get();
        // do stuff
    }
});

The second task won't execute until the first completes.

Java 5+ has many concurrent utilities for dealing with this kind of thing. This could mean using LinkedBlockingQueues, CountDownLatch or many, many others.

For an in-depth examination of concurrency Java Concurrency in Practice is a must-read.

Below is example for Inter thread communication:

public class Main {
    public static void main(String[] args) {
        Chat m = new Chat();
        new T1(m);
        new T2(m);
    }
}

class Chat {
    boolean flag = false;

    public synchronized void FromSam(String msg) {
        if (flag) {
            try {
                wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println(msg);
        flag = true;
        notify();
    }

    public synchronized void FromJam(String msg) {
        if (!flag) {
            try {
                wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        System.out.println(msg);
        flag = false;
        notify();
    }
}

class T1 implements Runnable {
    Chat m;
    String[] s1 = { "Hello Jam", "How are you ?", "I am also doing fine!" };

    public T1(Chat m1) {
        this.m = m1;
        new Thread(this, "Sam").start();
    }

    public void run() {
        for (int i = 0; i < s1.length; i++) {
            m.FromSam(s1[i]);
        }
    }
}

class T2 implements Runnable {
    Chat m;
    String[] s2 = { "HI Sam", "I am good,And U ?", "ha haa" };

    public T2(Chat m2) {
        this.m = m2;
        new Thread(this, "Jam").start();
    }

    public void run() {
        for (int i = 0; i < s2.length; i++) {
            m.FromJam(s2[i]);
        }
    }
}

Take a look at java.util.Observer/java.util.Observable. They are exactly what you are looking for.