java design pattern - Mediator pattern

调解人 调停
The major participants of the Mediator pattern are:
Mediator: Defines an interface for communicating with Colleague objects.
ConcreteMediator: implements cooperative behavior by coordinating Colleague objects,
it also knows and maintains its colleagues.
Colleague Classes: Each Colleague class knows its Mediator objects, Each colleague communicates with its mediator whenever it would have otherwise communicated with another colleague.

Mediator Pattern in JDK:
java.util.Timer class schedule XXX() methods.
java Concurrency Executor execute() method.
java.lang.reflect.Method invoke() method.

代码如下

package mediatorpattern;

/* Colleagure A wants to talk, and Colleague B to fight with mediator.
 * when they do some action(i.e., doSomething()),
 * they invoke mediator to do that.
 */


interface IMediator {
    public void talk();
    public void fight();
    public void registerA(ColleagueA a);
    public void registerB(ColleagueB b);
}


class MyConcreteMediator implements IMediator{
    ColleagueA talk;
    ColleagueB fight;

    @Override
    public void talk(){
        System.out.println("Mediator is talking");
        //let the talk colleague do some stuff
    }

    @Override
    public void fight(){
        System.out.println("Mediator is fighting");
        //let the fight colleague do some stuff
    }

    @Override
    public void registerA(ColleagueA a){
        this.talk = a;
    }

    @Override
    public void registerB(ColleagueB b){
        this.fight = b;
    }
}

abstract class Colleague{
    IMediator mediator;
    public abstract void doSomething();
}

class ColleagueA extends Colleague{
    public ColleagueA(IMediator mediator){
        this.mediator = mediator;
        this.mediator.registerA(this);
    }

    @Override
    public void doSomething(){
        this.mediator.talk();
    }
}

class ColleagueB extends Colleague{
    public ColleagueB(IMediator mediator){
        this.mediator = mediator;
        this.mediator.registerB(this);
    }

    @Override
    public void doSomething(){
        this.mediator.fight();
    }
}

public class MediatorPatternDemo{
    public static void main(String[] args){
        IMediator mediator = new MyConcreteMediator();

        ColleagueA talkColleague = new ColleagueA(mediator);
        ColleagueB fightColleague = new ColleagueB(mediator);

        talkColleague.doSomething();
        fightColleague.doSomething();
    }
}