07 adapter mode

Reprint of the original ：https://blog.csdn.net/sinat_21107433/article/details/102656617

You must have heard of “ network adapter ” Well ？ Also called network card . What is its function ？—— surf the internet ！

Such an answer is obviously not professional , The right answer is “ An important function of network card is serial connection / Parallel transformation . Because the communication between network card and LAN is carried out by serial transmission through cable or twisted pair , The communication between the network card and the computer is through the... On the computer motherboard I/O The bus is transmitted in parallel .”

You must ask ：“ What does this have to do with me ？”

Of course there is , Because you're learning design patterns , This is related to the adapter pattern to be introduced in this article ！

1. Brief Introduction

In addition to the network card adapter , You must have heard of power adapters ？ The voltage of domestic electricity in China is 220V, But our computers 、 mobile phone 、 Flat 、 The razor （ Rechargeable ） You won't use such a high voltage . This requires a power adapter （ The charger 、 transformer ）, Make various electronic devices and 220 Supply voltage of compatible . The power adapter acts as an adapter .

In software system design , When the classes that need to be combined are incompatible , Adapters like transformers are also needed to coordinate these incompatibilities , This is the adapter pattern ！

So what is the adapter pattern ？

Adapter pattern ：

Converts the interface of a class to another interface that the customer wants . The adapter pattern allows classes with incompatible interfaces to work together .

Similar to the power adapter , In the adapter pattern, there will be a design called “ Adapter ” The wrapper class , The object wrapped by the adapter is called Adapter . According to the definition , The adapter is based on the needs of customers , Convert the adapter's existing interface into another interface , Enables incompatible classes to work together .

2. Adapter pattern structure

The adapter pattern is divided into class adapter and object adapter .

• The adapter class （Adapter）： There is an inheritance or implementation relationship between the adapter and the adapter ;
• Adapter class （Adaptee）： There is an association between adapter and adapter .
• Target abstract class （Target）： Define the interface required by the customer .

Class adapter and object adapter UML The graph is as follows . Class adapter , The adapter class inherits the adapter class , And re implement the specific interface of the adapter to achieve the purpose of adapting the interface required by the customer . Object adapter , The adapter class instantiates an object of the adapter class in the class , And encapsulate it in the interface of the function required by the customer , Achieve the final adaptation purpose .

3. Adapter pattern code instance

Jungle The adapter pattern has been used many times in a project . Here is an example of using the object adapter pattern .

Path planning consists of two stages ： First, read and parse the drawing file , Get the point 、 Linear coordinates ; Secondly, calculate the processing path according to the demand . Software controller （Controller） On , System click “ Path planning ” The button automatically completes the above process .

Jungle A class has been encapsulated DxfParser, The suffix of the class name can be read dxf Drawing files for , And analyze the points 、 Line , Save to the path list . Another class PathPlanner Used to calculate the machining path .

In this case ,Controller Is the target abstract class ,DxfParser and PathPlanner It's an adapter class , The methods provided by these two classes can be used to meet the requirements of path planning . We just need to define another adapter class Adapter that will do .

3.1. Target abstract class

1. // Target abstract class

2. class Controller

3. {

4. public:

5. Controller(){}

6. virtual void pathPlanning() = 0;

7. private:

8. };

3.2. Adapter class

1. // Adapter class DxfParser

2. class DxfParser

3. {

4. public:

5. DxfParser(){}

6. void parseFile(){

7. printf(" Parse the file and extract the data \n");

8. }

9. };

10.  

11. // Adapter class PathPlanner

12. class PathPlanner

13. {

14. public:

15. PathPlanner(){}

16. void calculate(){

17. printf(" Calculate machining path \n");

18. }

19. };

3.3. The adapter class

1. // The adapter class Adapter

2. class Adapter:public Controller

3. {

4. public:

5. Adapter(){

6. dxfParser = new DxfParser();

7. pathPlanner = new PathPlanner();

8. }

9. void pathPlanning(){

10. printf(" Path planning ：\n");

11. dxfParser->parseFile();

12. pathPlanner->calculate();

13. }

14. private:

15. DxfParser *dxfParser;

16. PathPlanner *pathPlanner;

17. };

3.4. Client code example

1. #include <iostream>

2. #include "AdapterPattern.h"

3.  

4. int main()

5. {

6. Controller *controller = new Adapter();

7. controller->pathPlanning();

8.  

9. system("pause");

10. return 0;

11. }

3.5. effect

4. Adapter pattern summary

advantage ：

• Decouple the target class from the adapter class , Introduce an adapter class to realize code reuse , There is no need to modify the original structure ;
• Increase the transparency and reuse of classes , For clients , The adapter class is transparent ;
• Object adapters can adapt different adapters to the same target （ Object adapter ）;

shortcoming ：

• Restrictions on programming languages ：Java Multiple inheritance is not supported , At most one adapter class can be adapted at a time , Cannot fit multiple adapter classes at the same time ;

Apply to the environment ： 

• The system needs to use some existing classes , But the interfaces of these classes do not meet the needs of the system , Or there is no source code for these classes ;
• Want to create a reusable class , Used to work with classes that are not very related to each other .