Opening and closing principle

Definition

This principle has two characteristics , One is to say ‘ It's open to expansion （Open for extension）’, The other is that ‘ Closed for changes （Closed for modification）’[ASD].

【 Problem introduction 】

We need to deal with something , There are fixed steps ：a->b->c, But one day a customer has a need , An additional step should be added in certain cases , At this time, we should follow the principle of opening and closing , The original method logic should not be modified directly , Instead, write subclasses , To expand .

【 Code 】

BasicProcessing

package pers.keafmd.accumulate.designmode.openclosedprinciple;/** * Keafmd * * @ClassName: BasicProcessing * @Description: * @author:  Cowherd Conan  * @date: 2022-06-27 19:22 */public interface BasicProcessing {    void handle();}

BasicProcessingLogic

package pers.keafmd.accumulate.designmode.openclosedprinciple;/** * Keafmd * * @ClassName: BasicProcessingLogic * @Description:  Basic processing logic  * @author:  Cowherd Conan  * @date: 2022-06-27 19:19 */public class BasicProcessingLogic implements BasicProcessing{    public int num;    public BasicProcessingLogic() {        num = 10;    }    @Override    public void handle(){        System.out.println(" Processing steps a...");        System.out.println(" Processing steps b...");        System.out.println(" Processing steps c...");        System.out.println(num);    }}

CustomerSpecialProcessingLogic

package pers.keafmd.accumulate.designmode.openclosedprinciple;/** * Keafmd * * @ClassName: CustomerSpecialProcessingLogic * @Description:  Customer processing logic  * @author:  Cowherd Conan  * @date: 2022-06-27 19:21 */public class CustomerSpecialProcessingLogic extends BasicProcessingLogic{    @Override    public void handle(){        super.handle();    }    public void specialHandel(){        super.handle();        System.out.println(" Processing steps d...");    }}

OpenClosedPrincipleTest

package pers.keafmd.accumulate.designmode.openclosedprinciple;import java.util.Random;/** * Keafmd * * @ClassName: OpenClosedPrincipleTest * @Description:  Opening and closing principle  * @author:  Cowherd Conan  * @date: 2022-06-27 19:26 */public class OpenClosedPrincipleTest {    public static void main(String[] args) {        BasicProcessing  basicProcessing = new BasicProcessingLogic();        boolean flag = new Random().nextBoolean();;        if(flag){            basicProcessing.handle();        }else{            CustomerSpecialProcessingLogic processingLogic = new CustomerSpecialProcessingLogic();            processingLogic.specialHandel();        }    }}

The test results ：

Normal logic

 Processing steps a... Processing steps b... Processing steps c...10Process finished with exit code 0

Special logic ：

 Processing steps a... Processing steps b... Processing steps c...10 Processing steps d...Process finished with exit code 0

to open up - Closure principle is the core of object-oriented design . Following this principle can bring the huge benefits claimed by object-oriented technology , It's maintainable 、 Scalable 、 Reusable 、 Flexibility . Developers should abstract only those parts of the program that show frequent changes , However , It's also not a good idea to deliberately abstract every part of an application . It's just as important to reject the immature abstraction as the abstraction itself [ASD]. Bear in mind , Bear in mind