18) Mediator pattern

import java.util.ArrayList;
import java.util.List;

public class MediatorPatternDemo {

    public static void main(String[] args) {
        Mediator mediator = new Talkgroup();
        Talker talker1 = new Person(mediator, "Pankaj");
        Talker talker2 = new Person(mediator, "Lisa");
        Talker talker3 = new Person(mediator, "Saurabh");
        Talker talker4 = new Person(mediator, "David");
        mediator.addUser(talker1);
        mediator.addUser(talker2);
        mediator.addUser(talker3);
        mediator.addUser(talker4);

        talker1.send("Hi All");

    }
}

interface Mediator {

    public void sendMessage(String msg, Talker user);

    void addUser(Talker user);
}

abstract class Talker {
    protected Mediator mediator;
    protected String name;

    public Talker(Mediator med, String name) {
        this.mediator = med;
        this.name = name;
    }

    public abstract void send(String msg);

    public abstract void receive(String msg);
}

class Talkgroup implements Mediator {

    private List<Talker> TalkerList;

    public Talkgroup() {
        this.TalkerList = new ArrayList<Talker>();
    }

    @Override
    public void addUser(Talker talker) {
        this.TalkerList.add(talker);
    }

    @Override
    public void sendMessage(String msg, Talker talker) {
        for (Talker t : this.TalkerList) {
            // message should not be received by the user sending it
            if (t != talker) {
                t.receive(msg);
            }
        }
    }

}

class Person extends Talker {

    public Person(Mediator med, String name) {
        super(med, name);
    }

    @Override
    public void send(String msg) {
        System.out.println(this.name + " >>>>>>> " + msg);
        mediator.sendMessage(msg, this);
    }

    @Override
    public void receive(String msg) {
        System.out.println(this.name + " <<<<<<<< " + msg);
    }

}

Pankaj >>>>>>> Hi All
Lisa <<<<<<<< Hi All
Saurabh <<<<<<<< Hi All
David <<<<<<<< Hi All