package mediator_pattern;

public abstract class Mediator {
    public abstract void send(String message,Colleague colleague);
}

package mediator_pattern;

public class ConcreteMediator extends Mediator{
    private ConcreteColleague1 colleague1;
    private ConcreteColleague2 colleague2;
    public ConcreteColleague1 getColleague1() {
        return colleague1;
    }
    public void setColleague1(ConcreteColleague1 colleague1) {
        this.colleague1 = colleague1;
    }
    public ConcreteColleague2 getColleague2() {
        return colleague2;
    }
    public void setColleague2(ConcreteColleague2 colleague2) {
        this.colleague2 = colleague2;
    }
    
    @Override
    public void send(String message,Colleague colleague) {
        if(colleague == colleague1) {
            colleague2.notify(message);
        }else {
            colleague1.notify(message);
        }
    }
}

package mediator_pattern;

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

package mediator_pattern;

public class ConcreteColleague1 extends Colleague{
    public ConcreteColleague1(Mediator mediator) {
        super(mediator);
    }
    public void send(String message) {
        mediator.send(message, this);
    }
    public void notify(String message) {
        System.out.println("The colleague1 has the message:"+message);
    }
}

package mediator_pattern;

public class ConcreteColleague2 extends Colleague{
    public ConcreteColleague2(Mediator mediator) {
        super(mediator);
    }
    public void send(String message) {
        mediator.send(message, this);
    }
    public void notify(String message) {
        System.out.println("The colleague2 has the message:"+message);
    }
}

package mediator_pattern;

public class Main {
    public static void main(String args[]) {
        ConcreteMediator m = new ConcreteMediator();
        
        ConcreteColleague1 c1 = new ConcreteColleague1(m);
        ConcreteColleague2 c2 = new ConcreteColleague2(m);
        
        m.setColleague1(c1);
        m.setColleague2(c2);
        
        c1.send("Do you have the breakfast?");
        c2.send("No,do you want to invite me?");
    }
}
This is a general introduction to the 23 design patterns：
https://blog.csdn.net/GZHarryAnonymous/article/details/81567214