Design Pattern: Mediator Pattern in Java

Mediator pattern is used to restrict direct interaction between objects. A mediator class works as the middleman/communicator when one object wants to connect/use another object.

This article demonstrates Mediator pattern implementations in Java. Check the following examples.

Examples

Here are examples of Mediator pattern implementation-

Example #1: General Mediator

Let’s consider a general example.

Class Diagram

Take a look at the class diagram.

Mediator Interface

// IMediator.java

package com.bigboxcode.designpattern.mediator.mediator;

public interface IMediator {
    void sendMessage(Colleague colleague, String msg);
}

Mediator Class

// Mediator.java

package com.bigboxcode.designpattern.mediator.mediator;

public class Mediator implements IMediator {

    @Override
    public void sendMessage(Colleague receiver, String msg) {
        receiver.receiveMessage(msg);
    }

}

Colleague Abstract Class

// Colleague.java

package com.bigboxcode.designpattern.mediator.mediator;

public abstract class Colleague {
    protected Mediator mediator;

    public Colleague(Mediator mediator) {
        this.mediator = mediator;
    }

    public abstract void sendMessage(Colleague colleague, String message);

    public abstract void receiveMessage(String message);
}

Colleague1 Class

// Colleague1.java

package com.bigboxcode.designpattern.mediator.mediator;

public class Colleague1 extends Colleague{
    public Colleague1(Mediator mediator) {
        super(mediator);
    }

    @Override
    public void sendMessage(Colleague colleague, String msg) {
        mediator.sendMessage(colleague, msg);
    }

    @Override
    public void receiveMessage(String msg) {
        System.out.println("Message received in Colleague1: " + msg);
    }
}

Colleague2 Class

// Colleague2.java

package com.bigboxcode.designpattern.mediator.mediator;

public class Colleague2 extends Colleague {
    public Colleague2(Mediator mediator) {
        super(mediator);
    }

    @Override
    public void sendMessage(Colleague colleague, String msg) {
        mediator.sendMessage(colleague, msg);
    }

    @Override
    public void receiveMessage(String msg) {
        System.out.println("Message received in Colleague2: " + msg);
    }
}

Colleague3 Class

// Colleague3.java

package com.bigboxcode.designpattern.mediator.mediator;

public class Colleague3 extends Colleague {
    public Colleague3(Mediator mediator) {
        super(mediator);
    }

    @Override
    public void sendMessage(Colleague colleague, String msg) {
        mediator.sendMessage(colleague, msg);
    }

    @Override
    public void receiveMessage(String msg) {
        System.out.println("Message received in Colleague3: " + msg);
    }
}

Demo

// Demo.java

package com.bigboxcode.designpattern.mediator.mediator;

public class Demo {
    public static void main(String[] args) {
        Mediator mediator  = new Mediator();

        Colleague1 colleague1 = new Colleague1(mediator);
        Colleague2 colleague2 = new Colleague2(mediator);
        Colleague3 colleague3 = new Colleague3(mediator);

        colleague1.sendMessage(colleague2, "message from colleague1");

        System.out.println("-----------------------------------------------");

        colleague1.sendMessage(colleague3, "message from colleague1");

        System.out.println("-----------------------------------------------");

        colleague2.sendMessage(colleague3, "message from colleague2");

        System.out.println("-----------------------------------------------");

        colleague3.sendMessage(colleague1, "message from colleague3");

        System.out.println("-----------------------------------------------");

    }
}

Output

Message received in Colleague2: message from colleague1
-------------------------------------------------------------------------
Message received in Colleague3: message from colleague1
-------------------------------------------------------------------------
Message received in Colleague3: message from colleague2
-------------------------------------------------------------------------
Message received in Colleague1: message from colleague3
-------------------------------------------------------------------------

Source Code

Use the following link to get the source code:

Example	Source Code Link
Example #1: General Mediator	GitHub

Other Code Implementations

Use the following links to check Mediator pattern implementation in other programming languages.