设计模式七大原则之依赖倒转原则

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设计模式七大原则之依赖倒转原则

发布时间：『 2020-03-06 08:30』博客类别：23种设计模式阅读(600)

概念
高层模块不应该依赖低层模块，二者都应该依赖其抽象抽象不应该依赖细节，细节应该依赖抽象依赖倒转(倒置)的中心思想是面向接口编程低层模块尽量都要有抽象类或接口，或者两者都有，程序稳定性更好变量的声明类型尽量是抽象类或接口, 这样我们的变量引用和实际对象间，就存在一个缓冲层，利于程序扩展和优化

使用前

需求：老师通过不同的APP与学生聊天

实现老师通过微信、扣扣的方式，完成与学生互动需求；

package com.javaxl.design.rules.relyOn.before;

/**
 * @author 小李飞刀
 * @site www.javaxl.com
 * @company
 * @create  2020-02-16 11:51
 */
public class Teacher {
    public void receiveWeiXin(WeiXin weiXin){
        System.out.println(weiXin.getInfo());
    }

    public void receiveQQ(QQ qq){
        System.out.println(qq.getInfo());
    }
}

class WeiXin{
    public String info;

    public String getInfo() {
        return info;
    }

    public WeiXin(String info) {
        this.info = info;
    }
}

class QQ{
    public String info;

    public String getInfo() {
        return info;
    }

    public QQ(String info) {
        this.info = info;
    }
}


public class Client {
    public static void main(String[] args) {
        Teacher teacher = new Teacher();
        teacher.receiveQQ(new QQ("qq发送的消息"));
        teacher.receiveWeiXin(new WeiXin("微信发送的消息"));
    }
}

需求变更：老师新增了一个渠道“钉钉”获取学生的信息

package com.javaxl.design.rules.relyOn.beforePlus;

/**
 * @author 小李飞刀
 * @site www.javaxl.com
 * @company
 * @create  2020-02-16 11:51
 */
public class Teacher {
    public void receiveWeiXin(WeiXin weiXin){
        System.out.println(weiXin.getInfo());
    }

    public void receiveQQ(QQ qq){
        System.out.println(qq.getInfo());
    }

    public void receiveDing(DingDing dingDing){
        System.out.println(dingDing.getInfo());
    }
}

class WeiXin{
    private String info;

    public String getInfo() {
        return info;
    }

    public WeiXin(String info) {
        this.info = info;
    }
}

class QQ{
    private String info;

    public String getInfo() {
        return info;
    }

    public QQ(String info) {
        this.info = info;
    }
}

class DingDing{
    private String info;

    public String getInfo() {
        return info;
    }

    public DingDing(String info) {
        this.info = info;
    }
}

public class Client {
    public static void main(String[] args) {
        Teacher teacher = new Teacher();
        teacher.receiveQQ(new QQ("qq发送的消息"));
        teacher.receiveWeiXin(new WeiXin("微信发送的消息"));
        teacher.receiveDing(new DingDing("钉钉发送的消息"));
    }
}

使用后

实现老师通过微信、扣扣的方式，完成与学生互动需求；

package com.javaxl.design.rules.relyOn.after;

/**
 * @author 小李飞刀
 * @site www.javaxl.com
 * @company
 * @create  2020-02-16 12:01
 */
public class Teacher {
    public void receive(App app){
        System.out.println(app.getInfo());
    }
}
interface App{
    String getInfo();
}

class WinXin implements App{
    private String info;

    public WinXin(String info) {
        this.info = info;
    }

    @Override
    public String getInfo() {
        return info;
    }
}

class QQ implements App{
    private String info;

    public QQ(String info) {
        this.info = info;
    }

    @Override
    public String getInfo() {
        return info;
    }
}


public class Client {
    public static void main(String[] args) {
        Teacher teacher =new Teacher();
        teacher.receive(new WinXin("微信发来的消息"));
        teacher.receive(new QQ("qq发来的消息"));
    }
}

需求变更：老师新增了一个渠道“钉钉”获取学生的信息

package com.javaxl.design.rules.relyOn.afterPlus;

/**
 * @author 小李飞刀
 * @site www.javaxl.com
 * @company
 * @create  2020-02-16 12:01
 */
public class Teacher {
    public void receive(App app){
        System.out.println(app.getInfo());
    }
}

interface App{
    String getInfo();
}

class WinXin implements App {
    private String info;

    public WinXin(String info) {
        this.info = info;
    }

    @Override
    public String getInfo() {
        return info;
    }
}

class QQ implements App {
    private String info;

    public QQ(String info) {
        this.info = info;
    }

    @Override
    public String getInfo() {
        return info;
    }
}

class DingDing implements App {
    private String info;

    public DingDing(String info) {
        this.info = info;
    }

    @Override
    public String getInfo() {
        return info;
    }
}


public class Client {
    public static void main(String[] args) {
        Teacher teacher =new Teacher();
        teacher.receive(new WinXin("微信发来的消息"));
        teacher.receive(new QQ("qq发来的消息"));
        teacher.receive(new DingDing("钉钉发来的消息"));
    }
}

从上面可以看出

使用依赖倒转原则前：调用方-高层模块（Teacher类）依赖低层模块（WinXin类、QQ类），这样造成的后果就是，当低层模块扩展，需要高层模块做出一定的调整；这就违反了ocp原则；

使用依赖倒转原则后：调用方-高层模块（Teacher类）依赖低层模块对应的抽象（App接口），此时低层模块发生扩展，高层模块不受影响，这符合ocp原则；

over......

关键字： 设计模式

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