Java设计模式：（1）设计模式七大设计原则-依赖倒转原则

桑鱼

发布于 2020-03-17 15:12:24

4070

发布于 2020-03-17 15:12:24

文章被收录于专栏：学习笔记持续记录中...

基本介绍

1）依赖倒转原则基于这样的设计理念：相对于细节的多变形，抽象的东西要稳定的多，以抽象为基础搭建的架构比以细节为基础的架构要稳定的多

在Java中，抽象指的是接口或抽象类，细节就是具体的实现类

2）使用接口或抽象类的目的是制订好规范，而不涉及任何具体的操作，把展现细节的任务交给他们的实现类去完成

3）依赖倒转(倒置)的中心思想是面向接口编程

4）高层模块不应该依赖低层模块，二者都应该依赖其抽象

举个例子1

public class Inversion01 {
    public static void main(String[] args) {
        Person person = new Person();
        person.receive(new Email());

    }
}

class Email{
    public String getInfo(){
        return "Hello World";
    }
}

class Person{
    public void receive(Email email){
        System.out.println(email.getInfo());
    }
}

分析：在例子1中，类Person 中recevie()接口一个Email的对象的参数来接收消息，如果这个时候我们获取的对象增加了其他的方式，微信、短信，Persons也要增加接口方法

举个例子2

public class Inversion02 {
    public static void main(String[] args) {
        Person person = new Person();
        person.receive(new Email());
        person.receive(new WeiXin());
    }
}

interface IReceiver{
    public String getInfo();
}

class Email implements IReceiver{
    public String getInfo(){
        return "Hello Email ";
    }
}

class WeiXin implements IReceiver{
    public String getInfo(){
        return "Hello WeiXin ";
    }
}

class Person{
    public void receive(IReceiver iReceiver){
        System.out.println(iReceiver.getInfo());
    }
}

// 运行结果
Hello Email 
Hello WeiXin

分析：在例子2中，引入了一个抽象的接口IReceiver，表示接收者，Person类与IReceiver类发生依赖，然后Email和WeiXin各自实现IReceiver接口。这样就事项了依赖倒转原则

依赖关系传递的三种关系和应用案例

1. 通过接口传递实现依赖

public class Inversion03 {

    public static void main(String[] args) {
        OpenAndClose openAndClose = new OpenAndClose();
        openAndClose.open(new ChangHong());
    }
}

interface IOpenAndClose{
  public void open(ITV tv);
}

interface ITV{
  public void play();
}

class ChangHong implements ITV{
  public void play(){
    System.out.println("ChangHong is play");
  }
}

class OpenAndClose implements IOpenAndClose{
  public void open(ITV tv){
    tv.play();
  }
}

// 运行结果
ChangHong is play

2. 通过构造方法依赖传递

public class Inversion04 {
    public static void main(String[] args) {
        OpenAndClass openAndClass = new OpenAndClass(new ChangHong());
        openAndClass.open();
    }
}

interface IOpenAndClose{
    public void open();
}

interface ITV{
    public void play();
}

class OpenAndClass implements IOpenAndClose{
    public ITV tv;
    public OpenAndClass(ITV tv){
        this.tv = tv;
    }
    public void open(){
        this.tv.play();
    }
}

class ChangHong implements ITV{
    public void play(){
        System.out.println("ChangHong is play");
    }
}

// 运行结果
ChangHong is play

3. 通过setter方法传递

public class Inversion05 {
    public static void main(String[] args) {
        OpenAndClose openAndClose = new OpenAndClose();
        openAndClose.setTv(new ChangHong());
        openAndClose.open();
    }
}

interface IOpenAndClose{
    public void open();
    public void setTv(ITV tv);
}

interface ITV{
    public void play();
}

class OpenAndClose implements IOpenAndClose{
    private ITV tv;
    public void setTv(ITV tv){
        this.tv = tv;
    }

    public void open(){
        this.tv.play();
    }
}

class ChangHong implements ITV{
    public void play(){
        System.out.println("ChangHong is play");
    }
}
// 运行结果
ChangHong is play

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