中介模式,又叫 调停者模式 Mediator
包装了一系列对象相互作用的方式,使得这些对象不必相互明显引用,降低耦合
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问题:
image.png -
调停者模式效果
image.png
鸡蛋都放一个篮子里了??
- 物以类聚,人以群分.这个模式分类的度狠重要
- 虽然在架构设计里这种方式很危险,但是敲代码的时候能做到这种效果还是很难得的.
调停者所协调的对象叫同事(Colleague)对象
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上类图:
调停者模式.png
违反开闭原则,加一个同事要在Mediator里面添加一个属性和对应的操作.
优点:化繁为简,最大程度的支持了迪米特法则
缺点:调停者类狠复杂,而且代码很难复用
设计模式虽好,但不能滥用
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代码示例:
1: 创建一个抽象同事类角色接口
package com.byedbl.mediator;
/**
* An abstract colleague
*/
public interface Colleague {
void change();
void action();
}
- 创建3个同事
package com.byedbl.mediator;
/**
* A concrete colleague
*/
public class ColleagueA implements Colleague {
private final String type = "A";
private Mediator med;
public ColleagueA(Mediator m) {
med = m;
med.register(this, type);
}
@Override
public void change() {
System.out.println("----- A changed now ! -----");
med.changed(type);
}
@Override
public void action() {
System.out.println(" A is changed by mediator ");
}
}
package com.byedbl.mediator;
/**
* A concrete colleague
*/
public class ColleagueB implements Colleague {
private final String type = "B";
private Mediator med;
public ColleagueB(Mediator m) {
med = m;
med.register(this, type);
}
@Override
public void change() {
System.out.println("----- B changed now ! -----");
med.changed(type);
}
@Override
public void action() {
System.out.println(" B is changed by mediator ");
}
}
package com.byedbl.mediator;
/**
* A concrete colleague
*/
public class ColleagueC implements Colleague {
private final String type = "C";
private Mediator med;
public ColleagueC(Mediator m) {
med = m;
med.register(this, type);
}
@Override
public void change() {
System.out.println("----- C changed now ! -----");
med.changed(type);
}
@Override
public void action() {
System.out.println(" C is changed by mediator ");
}
}
- 定义一个抽象调停者角色
package com.byedbl.mediator;
/**
* An abstract Mediator
*/
public interface Mediator {
public void register(Colleague c, String type);
public void changed(String type);
}
- 实现了一个管理所有的同事的复杂调停者类,
package com.byedbl.mediator;
/**
* A concrete mediator
*/
public class ConcreteMediator implements Mediator {
private ColleagueA a;
private ColleagueB b;
private ColleagueC c;
public ConcreteMediator() {
}
@Override
public void register(Colleague colleague, String type) {
if (type == "A") {
a = (ColleagueA) colleague;
} else if (type == "B") {
b = (ColleagueB) colleague;
} else if (type == "C") {
c = (ColleagueC) colleague;
}
}
@Override
public void changed(String type) {
if (type == "A") {
b.action();
c.action();
} else if (type == "B") {
a.action();
c.action();
} else if (type == "C") {
a.action();
b.action();
}
}
}
- 客户端用法
package com.byedbl.mediator;
/**
* A test client
*/
public class Test {
public static void main(String[] args) {
Mediator myMed = new ConcreteMediator();
ColleagueA a = new ColleagueA(myMed);
ColleagueB b = new ColleagueB(myMed);
ColleagueC c = new ColleagueC(myMed);
a.change();
System.out.println("----------------");
b.change();
System.out.println("****************");
c.change();
}
}
这个模式的最大问题是调停者,正所谓成也调停败也调停.管的多,知道的太多也是缺点.
