1.什么是依赖倒转原则？

2.代码案例

package com.szh.principle.inversion;

/**
 *
 */
class Email {
    public String getInfo() {
        return "电子邮件信息: hello,world";
    }
}

// 完成Person接收消息的功能
// 方式1分析
//   1. 简单，比较容易想到
//   2. 如果我们获取的对象是 微信，短信等等，则新增类，同时Person也要增加相应的接收方法
//   3. 解决思路：引入一个抽象的接口IReceiver, 表示接收者, 这样Person类与接口IReceiver发生依赖
//   因为Email, WeiXin 等等属于接收的范围，他们各自实现IReceiver 接口就ok, 这样我们就符号依赖倒转原则
class Person {
    public void receive(Email email ) {
        System.out.println(email.getInfo());
    }
}

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

package com.szh.principle.inversion.improve;

/**
 *
 */
//定义接口
interface IReceiver {
    public String getInfo();
}

class Email implements IReceiver {
    public String getInfo() {
        return "电子邮件信息: hello,world";
    }
}

//增加微信
class WeiXin implements IReceiver {
    public String getInfo() {
        return "微信信息: hello,ok";
    }
}

//方式2
class Person {
    //这里我们是对接口的依赖
    public void receive(IReceiver receiver ) {
        System.out.println(receiver.getInfo());
    }
}

public class DependencyInversion {
    public static void main(String[] args) {
        //客户端无需改变
        Person person = new Person();
        person.receive(new Email());
        person.receive(new WeiXin());
    }
}

3.依赖关系传递的三种方式和案例举例

3.1 接口传递

package com.szh.principle.inversion.improve;

/**
 * 方式1: 通过接口传递实现依赖
 */
 interface IOpenAndClose1 {
    public void open(ITV1 tv); //抽象方法,接收接口
 }

 interface ITV1 { //ITV接口
    public void play();
 }

class OpenAndClose1 implements IOpenAndClose1 {
     @Override
     public void open(ITV1 tv){
         tv.play();
     }
}

 class ChangHong1 implements ITV1 {
	@Override
	public void play() {
		System.out.println("长虹电视机，打开");
	}
 }

public class DependencyPass1 {
    public static void main(String[] args) {
        ChangHong1 changHong = new ChangHong1();
		OpenAndClose1 openAndClose = new OpenAndClose1();
		openAndClose.open(changHong);
    }
}

3.2 构造方法传递

package com.szh.principle.inversion.improve;

/**
 * 方式2: 通过构造方法依赖传递
 */
 interface IOpenAndClose2 {
    public void open(); //抽象方法
 }

 interface ITV2 { //ITV接口
    public void play();
 }

 class OpenAndClose2 implements IOpenAndClose2 {
    public ITV2 tv; //成员

    public OpenAndClose2(ITV2 tv){ //构造器
        this.tv = tv;
    }

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

class ChangHong2 implements ITV2 {
    public void play() {
        System.out.println("长虹电视机，打开");
    }
}

public class DependencyPass2 {
    public static void main(String[] args) {
        ChangHong2 changHong = new ChangHong2();
        //通过构造器进行依赖传递
		OpenAndClose2 openAndClose = new OpenAndClose2(changHong);
		openAndClose.open();
    }
}

3.3 setter方法传递

package com.szh.principle.inversion.improve;

/**
 * 方式3: 通过setter方法传递
 */
interface IOpenAndClose3 {
    public void open(); // 抽象方法
    public void setTv(ITV3 tv);
}

interface ITV3 { // ITV接口
    public void play();
}

class OpenAndClose3 implements IOpenAndClose3 {
    private ITV3 tv;

    public void setTv(ITV3 tv) {
        this.tv = tv;
    }

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

class ChangHong3 implements ITV3 {
    public void play() {
        System.out.println("长虹电视机，打开");
    }
}

public class DependencyPass3 {
    public static void main(String[] args) {
        ChangHong3 changHong = new ChangHong3();
        //通过setter方法进行依赖传递
        OpenAndClose3 openAndClose = new OpenAndClose3();
        openAndClose.setTv(changHong);
        openAndClose.open();
    }
}