複数のオブジェクト(Colleague)の制御を行うのにMediatorクラスを作成し、これを介して制御を行います。

package org.example.mediator;

public interface Mediator {
    public void createColleagues();
    public void colleagueChanged();
}

package org.example.mediator;

public abstract class Colleague {
    protected Mediator mediator;
    public abstract void setMediator(Mediator mediator);
    public abstract void controlColleague();
}

package org.example.mediator;

public class ConcreteColleague1 extends Colleague {
    @Override
    public void setMediator(Mediator mediator) {
        this.mediator = mediator;
    }

    @Override
    public void controlColleague() {
    }
}

package org.example.mediator;

public class ConcreteColleague2 extends Colleague {
    @Override
    public void setMediator(Mediator mediator)
    {
        this.mediator = mediator;
    }

    @Override
    public void controlColleague()
    {
    }
}

package org.example.mediator;

public class ConcreteMediator implements Mediator{
    private Colleague concreteColleague1;
    private Colleague concreteColleague2;

    @Override
    public void createColleagues() {
        concreteColleague1 = new ConcreteColleague1();
        concreteColleague1.setMediator(this);
        concreteColleague2 = new ConcreteColleague1();
        concreteColleague2.setMediator(this);
    }

    @Override
    public void colleagueChanged() {
        concreteColleague1.controlColleague();
        concreteColleague2.controlColleague();
    }
}

package org.example.mediator;

import java.util.Scanner;

public class Main {
    public static void main(String[] args)
    {
        Mediator mediator = new ConcreteMediator();
        mediator.createColleagues();
        mediator.colleagueChanged();
    }
}