设计模式之中介者模式讲解

概念：也称为调停者模式。用一个中介者对象封装一系列对象的交互，中介者使各对象不需要显示地相互作用，从而使其耦合松散，而且可以独立地改变它们之间的交互。

• 抽象中介者：定义中介者的操作。
• 具体中介者：实现抽象中介者定义的操作，并持有被调停者对象。
• 抽象被调停者：定义被调停者的操作。
• 具体被调停者：实现具体操作，通过中介者进行交互。

以下用一个同事之间沟通的例子来帮助大家理解。

public interface Mediator {
    void changed(Colleague colleague);
    void register(Colleague colleague);
}
 
public interface Colleague {
    void send(String message);
    void receive(String message);
}
 
public class ConcreteMediator implements Mediator {
    private List<Colleague> colleagues = new ArrayList<>();
    public void register(Colleague colleague) {
        colleagues.add(colleague);
    }
    @Override
    public void changed(Colleague colleague) {
        // 假设每个同事收到消息后都向所有其他同事发送消息
        for (Colleague c : colleagues) {
            if (!c.equals(colleague)) {
                c.receive("Message from " + colleague.getClass().getSimpleName());
            }
        }
    }
}
 
public class ConcreteColleagueA implements Colleague {
    private Mediator mediator;
    public ConcreteColleagueA(Mediator mediator) {
        this.mediator = mediator;
        mediator.register(this);
    }
    @Override
    public void send(String message) {
        System.out.println("Colleague A sends: " + message);
        mediator.changed(this);
    }
    @Override
    public void receive(String message) {
        System.out.println("Colleague A receives: " + message);
    }
}
 
public class ConcreteColleagueB implements Colleague {
    private Mediator mediator;
    public ConcreteColleagueB(Mediator mediator) {
        this.mediator = mediator;
        mediator.register(this);
    }
    @Override
    public void send(String message) {
        System.out.println("Colleague B sends: " + message);
        mediator.changed(this);
    }
    @Override
    public void receive(String message) {
        System.out.println("Colleague B receives: " + message);
    }
}
 
public class Demo {
    public static void main(String[] args) {
        ConcreteMediator mediator = new ConcreteMediator();
        Colleague colleagueA = new ConcreteColleagueA(mediator);
        Colleague colleagueB = new ConcreteColleagueB(mediator);
        colleagueA.send("Hello from A");
        colleagueB.send("Hello from B");
    }
}

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