基本介绍

依赖倒转原则是指：

  1. 高层模块不应该依赖底层模块，二者都应该依赖其抽象
  2. 抽象不应该依赖细节，细节应该依赖抽象
  3. 依赖倒转（倒置）的中心思想是面向接口编程
  4. 依赖倒转原则是基于真阳的设计理念：相对于细节的多变性，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

  5. 使用接口或抽象类的目的是制定好的规范，而不设计任何的具体操作，把展现的细节任务交给他们实现类去完成

    实例应用

    方案一：

    ```java public class Application {

    public static void main(String[] args) {

    1.  Person person = new Person();
    2.  person.run(new Email());

    } }

class Email { public void getInfo(){ System.out.println(“邮件信息：hello world”); } } class Person { //没有可用性 简单比较容易想到 //如果我们想过去的对象是微信，短信等，则需要新增类或者是新增方法 //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 public void run(Email email){ email.getInfo(); } }

  1. 运行结果：
  2. ```java
  3. "F:\Program Files\Java\jdk1.8.0_201\bin\java.exe" "-javaagent:F:\Program Files\JetBrains\IntelliJ IDEA 2018.3\lib\idea_rt.jar=53831:F:\Program Files\JetBrains\IntelliJ IDEA 2018.3\bin" -Dfile.encoding=UTF-8 -classpath "F:\Program Files\Java\jdk1.8.0_201\jre\lib\charsets.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\deploy.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\access-bridge-64.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\cldrdata.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\dnsns.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\jaccess.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\jfxrt.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\localedata.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\nashorn.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunec.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunjce_provider.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunmscapi.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunpkcs11.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\zipfs.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\javaws.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\jce.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\jfr.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\jfxswt.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\jsse.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\management-agent.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\plugin.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\resources.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\rt.jar;E:\study\study_jvm\target\classes;F:\JAVA\Maven\Repository\org\springframework\boot\spring-boot-starter-web\2.4.1\spring-boot-starter-web-2.4.1.jar;F:\JAVA\Maven\Repository\org\springframework\boot\spring-boot-starter\2.4.1\spring-boot-starter-2.4.1.jar;F:\JAVA\Maven\Repository\org\springframework\boot\spring-boot\2.4.1\spring-boot-2.4.1.jar;F:\JAVA\Maven\Repository\org\springframework\boot\spring-boot-autoconfigure\2.4.1\spring-boot-autoconfigure-2.4.1.jar;F:\JAVA\Maven\Repository\org\springframework\boot\spring-boot-starter-logging\2.4.1\spring-boot-starter-logging-2.4.1.jar;F:\JAVA\Maven\Repository\ch\qos\logback\logback-classic\1.2.3\logback-classic-1.2.3.jar;F:\JAVA\Maven\Repository\ch\qos\logback\logback-core\1.2.3\logback-core-1.2.3.jar;F:\JAVA\Maven\Repository\org\apache\logging\log4j\log4j-to-slf4j\2.13.3\log4j-to-slf4j-2.13.3.jar;F:\JAVA\Maven\Repository\org\apache\logging\log4j\log4j-api\2.13.3\log4j-api-2.13.3.jar;F:\JAVA\Maven\Repository\org\slf4j\jul-to-slf4j\1.7.30\jul-to-slf4j-1.7.30.jar;F:\JAVA\Maven\Repository\jakarta\annotation\jakarta.annotation-api\1.3.5\jakarta.annotation-api-1.3.5.jar;F:\JAVA\Maven\Repository\org\yaml\snakeyaml\1.27\snakeyaml-1.27.jar;F:\JAVA\Maven\Repository\org\springframework\boot\spring-boot-starter-json\2.4.1\spring-boot-starter-json-2.4.1.jar;F:\JAVA\Maven\Repository\com\fasterxml\jackson\core\jackson-databind\2.11.3\jackson-databind-2.11.3.jar;F:\JAVA\Maven\Repository\com\fasterxml\jackson\core\jackson-annotations\2.11.3\jackson-annotations-2.11.3.jar;F:\JAVA\Maven\Repository\com\fasterxml\jackson\core\jackson-core\2.11.3\jackson-core-2.11.3.jar;F:\JAVA\Maven\Repository\com\fasterxml\jackson\datatype\jackson-datatype-jdk8\2.11.3\jackson-datatype-jdk8-2.11.3.jar;F:\JAVA\Maven\Repository\com\fasterxml\jackson\datatype\jackson-datatype-jsr310\2.11.3\jackson-datatype-jsr310-2.11.3.jar;F:\JAVA\Maven\Repository\com\fasterxml\jackson\module\jackson-module-parameter-names\2.11.3\jackson-module-parameter-names-2.11.3.jar;F:\JAVA\Maven\Repository\org\springframework\boot\spring-boot-starter-tomcat\2.4.1\spring-boot-starter-tomcat-2.4.1.jar;F:\JAVA\Maven\Repository\org\apache\tomcat\embed\tomcat-embed-core\9.0.41\tomcat-embed-core-9.0.41.jar;F:\JAVA\Maven\Repository\org\glassfish\jakarta.el\3.0.3\jakarta.el-3.0.3.jar;F:\JAVA\Maven\Repository\org\apache\tomcat\embed\tomcat-embed-websocket\9.0.41\tomcat-embed-websocket-9.0.41.jar;F:\JAVA\Maven\Repository\org\springframework\spring-web\5.3.2\spring-web-5.3.2.jar;F:\JAVA\Maven\Repository\org\springframework\spring-beans\5.3.2\spring-beans-5.3.2.jar;F:\JAVA\Maven\Repository\org\springframework\spring-webmvc\5.3.2\spring-webmvc-5.3.2.jar;F:\JAVA\Maven\Repository\org\springframework\spring-aop\5.3.2\spring-aop-5.3.2.jar;F:\JAVA\Maven\Repository\org\springframework\spring-context\5.3.2\spring-context-5.3.2.jar;F:\JAVA\Maven\Repository\org\springframework\spring-expression\5.3.2\spring-expression-5.3.2.jar;F:\JAVA\Maven\Repository\org\projectlombok\lombok\1.18.16\lombok-1.18.16.jar;F:\JAVA\Maven\Repository\org\slf4j\slf4j-api\1.7.30\slf4j-api-1.7.30.jar;F:\JAVA\Maven\Repository\org\springframework\spring-core\5.3.2\spring-core-5.3.2.jar;F:\JAVA\Maven\Repository\org\springframework\spring-jcl\5.3.2\spring-jcl-5.3.2.jar" design.Application
  4. 邮件信息：hello world

方案二：

  1. public class Application {
  3.     public static void main(String[] args)  {
  4.         Person person = new Person();
  5.         person.run(new Email());
  6.         person.run(new WeiXin());
  7.     }
  8. }
  10. interface IReceiver{
  11.     public void getInfo();
  12. }
  13. class Email implements IReceiver{
  14.     public void getInfo(){
  15.         System.out.println("邮件信息：hello world");
  16.     }
  17. }
  18. class WeiXin implements IReceiver{
  19.     public void getInfo(){
  20.         System.out.println("微信信息：hello world");
  21.     }
  22. }
  23. class Person {
  24.     public void run(IReceiver receiver){
  25.         receiver.getInfo();
  26.     }
  27. }

运行结果：

  1. "F:\Program Files\Java\jdk1.8.0_201\bin\java.exe" "-javaagent:F:\Program Files\JetBrains\IntelliJ IDEA 2018.3\lib\idea_rt.jar=53988:F:\Program Files\JetBrains\IntelliJ IDEA 2018.3\bin" -Dfile.encoding=UTF-8 -classpath "F:\Program Files\Java\jdk1.8.0_201\jre\lib\charsets.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\deploy.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\access-bridge-64.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\cldrdata.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\dnsns.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\jaccess.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\jfxrt.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\localedata.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\nashorn.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunec.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunjce_provider.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunmscapi.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunpkcs11.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\zipfs.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\javaws.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\jce.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\jfr.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\jfxswt.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\jsse.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\management-agent.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\plugin.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\resources.jar;F:\Program Files\Java\jdk1.8.0_201\jre\lib\rt.jar;E:\study\study_jvm\target\classes;F:\JAVA\Maven\Repository\org\springframework\boot\spring-boot-starter-web\2.4.1\spring-boot-starter-web-2.4.1.jar;F:\JAVA\Maven\Repository\org\springframework\boot\spring-boot-starter\2.4.1\spring-boot-starter-2.4.1.jar;F:\JAVA\Maven\Repository\org\springframework\boot\spring-boot\2.4.1\spring-boot-2.4.1.jar;F:\JAVA\Maven\Repository\org\springframework\boot\spring-boot-autoconfigure\2.4.1\spring-boot-autoconfigure-2.4.1.jar;F:\JAVA\Maven\Repository\org\springframework\boot\spring-boot-starter-logging\2.4.1\spring-boot-starter-logging-2.4.1.jar;F:\JAVA\Maven\Repository\ch\qos\logback\logback-classic\1.2.3\logback-classic-1.2.3.jar;F:\JAVA\Maven\Repository\ch\qos\logback\logback-core\1.2.3\logback-core-1.2.3.jar;F:\JAVA\Maven\Repository\org\apache\logging\log4j\log4j-to-slf4j\2.13.3\log4j-to-slf4j-2.13.3.jar;F:\JAVA\Maven\Repository\org\apache\logging\log4j\log4j-api\2.13.3\log4j-api-2.13.3.jar;F:\JAVA\Maven\Repository\org\slf4j\jul-to-slf4j\1.7.30\jul-to-slf4j-1.7.30.jar;F:\JAVA\Maven\Repository\jakarta\annotation\jakarta.annotation-api\1.3.5\jakarta.annotation-api-1.3.5.jar;F:\JAVA\Maven\Repository\org\yaml\snakeyaml\1.27\snakeyaml-1.27.jar;F:\JAVA\Maven\Repository\org\springframework\boot\spring-boot-starter-json\2.4.1\spring-boot-starter-json-2.4.1.jar;F:\JAVA\Maven\Repository\com\fasterxml\jackson\core\jackson-databind\2.11.3\jackson-databind-2.11.3.jar;F:\JAVA\Maven\Repository\com\fasterxml\jackson\core\jackson-annotations\2.11.3\jackson-annotations-2.11.3.jar;F:\JAVA\Maven\Repository\com\fasterxml\jackson\core\jackson-core\2.11.3\jackson-core-2.11.3.jar;F:\JAVA\Maven\Repository\com\fasterxml\jackson\datatype\jackson-datatype-jdk8\2.11.3\jackson-datatype-jdk8-2.11.3.jar;F:\JAVA\Maven\Repository\com\fasterxml\jackson\datatype\jackson-datatype-jsr310\2.11.3\jackson-datatype-jsr310-2.11.3.jar;F:\JAVA\Maven\Repository\com\fasterxml\jackson\module\jackson-module-parameter-names\2.11.3\jackson-module-parameter-names-2.11.3.jar;F:\JAVA\Maven\Repository\org\springframework\boot\spring-boot-starter-tomcat\2.4.1\spring-boot-starter-tomcat-2.4.1.jar;F:\JAVA\Maven\Repository\org\apache\tomcat\embed\tomcat-embed-core\9.0.41\tomcat-embed-core-9.0.41.jar;F:\JAVA\Maven\Repository\org\glassfish\jakarta.el\3.0.3\jakarta.el-3.0.3.jar;F:\JAVA\Maven\Repository\org\apache\tomcat\embed\tomcat-embed-websocket\9.0.41\tomcat-embed-websocket-9.0.41.jar;F:\JAVA\Maven\Repository\org\springframework\spring-web\5.3.2\spring-web-5.3.2.jar;F:\JAVA\Maven\Repository\org\springframework\spring-beans\5.3.2\spring-beans-5.3.2.jar;F:\JAVA\Maven\Repository\org\springframework\spring-webmvc\5.3.2\spring-webmvc-5.3.2.jar;F:\JAVA\Maven\Repository\org\springframework\spring-aop\5.3.2\spring-aop-5.3.2.jar;F:\JAVA\Maven\Repository\org\springframework\spring-context\5.3.2\spring-context-5.3.2.jar;F:\JAVA\Maven\Repository\org\springframework\spring-expression\5.3.2\spring-expression-5.3.2.jar;F:\JAVA\Maven\Repository\org\projectlombok\lombok\1.18.16\lombok-1.18.16.jar;F:\JAVA\Maven\Repository\org\slf4j\slf4j-api\1.7.30\slf4j-api-1.7.30.jar;F:\JAVA\Maven\Repository\org\springframework\spring-core\5.3.2\spring-core-5.3.2.jar;F:\JAVA\Maven\Repository\org\springframework\spring-jcl\5.3.2\spring-jcl-5.3.2.jar" design.Application
  2. 邮件信息：hello world
  3. 微信信息：hello world

依赖关系传递的三种方式

构造器传入

  1. public class Application {
  3.     public static void main(String[] args)  {
  4.         Person person = new Person(new WeiXin());
  5.         person.run();
  6.     }
  7. }
  9. interface IReceiver{
  10.     public void getInfo();
  11. }
  12. class Email implements IReceiver{
  13.     public void getInfo(){
  14.         System.out.println("邮件信息：hello world");
  15.     }
  16. }
  17. class WeiXin implements IReceiver{
  18.     public void getInfo(){
  19.         System.out.println("微信信息：hello world");
  20.     }
  21. }
  22. class Person {
  23.     private IReceiver receiver;
  25.     public Person(IReceiver receiver) {
  26.         this.receiver = receiver;
  27.     }
  29.     public void run(){
  30.         receiver.getInfo();
  31.     }
  32. }

接口传入

  1. public class Application {
  3.     public static void main(String[] args)  {
  4.         Person person = new Person();
  5.         person.run(new Email());
  6.         person.run(new WeiXin());
  7.     }
  8. }
  10. interface IReceiver{
  11.     public void getInfo();
  12. }
  13. class Email implements IReceiver{
  14.     public void getInfo(){
  15.         System.out.println("邮件信息：hello world");
  16.     }
  17. }
  18. class WeiXin implements IReceiver{
  19.     public void getInfo(){
  20.         System.out.println("微信信息：hello world");
  21.     }
  22. }
  23. class Person {
  24.     public void run(IReceiver receiver){
  25.         receiver.getInfo();
  26.     }
  27. }

setter传入

  1. public class Application {
  3.     public static void main(String[] args)  {
  4.         Person person = new Person();
  5.         person.setReceiver(new WeiXin());
  6.         person.run();
  7.     }
  8. }
  10. interface IReceiver{
  11.     void getInfo();
  12. }
  13. class WeiXin implements IReceiver{
  14.     public void getInfo(){
  15.         System.out.println("微信信息：hello world");
  16.     }
  17. }
  18. class Person {
  19.     private IReceiver receiver;
  21.     public void setReceiver(IReceiver receiver) {
  22.         this.receiver = receiver;
  23.     }
  25.     public void run(){
  26.         receiver.getInfo();
  27.     }
  28. }

依赖倒转原则注意事项和细节

  1. 底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。
  2. 变量的生命类型尽量都是抽象类或接口，这样我们的变量引用和实际对象间，就存在一个缓冲层，利于程序的扩展和优化
  3. 继承时遵循里氏替换原则