Java - Inter Thread Communication

If you are aware of interprocess communication then it will be easy for you to understand interthread communication.

Inter-thread Communication in Java

Inter-thread communication is important when you develop an application where two or more threads exchange some information. Inter-thread communication is achieved by using the wait(), notify(), and notifyAll() methods of the Object class.

Methods used for Inter-thread Communication

There are three simple methods and a little trick which makes thread communication possible. All the three methods are listed below −

These methods have been implemented as final methods in Object, so they are available in all the classes. All three methods can be called only from within a synchronized context.

Example of Inter-thread Communication in Java

This examples shows how two threads can communicate using wait() and notify() method. You can create a complex system using the same concept.

 class Chat { boolean flag = false; public synchronized void Question(String msg) { if (flag) { try { wait(); } catch (InterruptedException e) { e.printStackTrace(); } } System.out.println(msg); flag = true; notify(); } public synchronized void Answer(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 = { "Hi", "How are you ?", "I am also doing fine!" }; public T1(Chat m1) { this.m = m1; new Thread(this, "Question").start(); } public void run() { for (int i = 0; i < s1.length; i++) { m.Question(s1[i]); } } } class T2 implements Runnable { Chat m; String[] s2 = { "Hi", "I am good, what about you?", "Great!" }; public T2(Chat m2) { this.m = m2; new Thread(this, "Answer").start(); } public void run() { for (int i = 0; i < s2.length; i++) { m.Answer(s2[i]); } } } public class TestThread { public static void main(String[] args) { Chat m = new Chat(); new T1(m); new T2(m); } } 

When the above program is complied and executed, it produces the following result −

Output

 Hi Hi How are you ? I am good, what about you? I am also doing fine! Great!