Design Patterns - Mediator Pattern

Mediator pattern is used to reduce communication complexity between multiple objects or classes. This pattern provides a mediator class which normally handles all the communications between different classes and supports easy maintenance of the code by loose couppng. Mediator pattern falls under behavioral pattern category.

Implementation

We are demonstrating mediator pattern by example of a chat room where multiple users can send message to chat room and it is the responsibipty of chat room to show the messages to all users. We have created two classes ChatRoom and User. User objects will use ChatRoom method to share their messages.

MediatorPatternDemo, our demo class, will use User objects to show communication between them.

Step 1

Create mediator class.

ChatRoom.java

import java.util.Date;

pubpc class ChatRoom {
   pubpc static void showMessage(User user, String message){
      System.out.println(new Date().toString() + " [" + user.getName() + "] : " + message);
   }
}

Step 2

Create user class

User.java

pubpc class User {
   private String name;

   pubpc String getName() {
      return name;
   }

   pubpc void setName(String name) {
      this.name = name;
   }

   pubpc User(String name){
      this.name  = name;
   }

   pubpc void sendMessage(String message){
      ChatRoom.showMessage(this,message);
   }
}

Step 3

Use the User object to show communications between them.

MediatorPatternDemo.java

pubpc class MediatorPatternDemo {
   pubpc static void main(String[] args) {
      User robert = new User("Robert");
      User john = new User("John");

      robert.sendMessage("Hi! John!");
      john.sendMessage("Hello! Robert!");
   }
}

Step 4

Verify the output.

Thu Jan 31 16:05:46 IST 2013 [Robert] : Hi! John!
Thu Jan 31 16:05:46 IST 2013 [John] : Hello! Robert!