《设计模式的艺术》笔记

介绍

适配器模式将一个接口转换成客户希望的另一个接口，使接口不兼容的那些类可以一起工作，其别名为包装器。

实现

对象适配器模式

myclass.h

//
// Created by yuwp on 2024/1/12.
//#ifndef DESIGNPATTERNS_MYCLASS_H
#define DESIGNPATTERNS_MYCLASS_H#include <iostream>class Target {  // 目标类
public:virtual void request() = 0;
};class Adaptee {     // 适配者类
public:void specificRequest();
};class Adapter : public Target { // 适配器类
public:Adapter(Adaptee *adaptee);void request() override;private:Adaptee *m_adaptee;
};#endif //DESIGNPATTERNS_MYCLASS_H

myclass.cpp

//
// Created by yuwp on 2024/1/12.
//#include "myclass.h"Adapter::Adapter(Adaptee *adaptee) {m_adaptee = adaptee;
}void Adapter::request() {if (m_adaptee) {m_adaptee->specificRequest();}
}void Adaptee::specificRequest() {std::cout << "Adaptee被适配" << std::endl;
}

main.cpp

#include <iostream>
#include <mutex>
#include "myclass.h"int main() {Adaptee *adaptee = new Adaptee;Target *target = new Adapter(adaptee);target->request();delete target;delete adaptee;return 0;
}

类适配器模式

myclass.h

//
// Created by yuwp on 2024/1/12.
//#ifndef DESIGNPATTERNS_MYCLASS_H
#define DESIGNPATTERNS_MYCLASS_H#include <iostream>class Target {  // 目标类
public:virtual void request() = 0;
};class Adaptee {     // 适配者类
public:void specificRequest();
};class Adapter : public Target, public Adaptee { // 适配器类
public:void request() override;};#endif //DESIGNPATTERNS_MYCLASS_H

myclass.cpp

//
// Created by yuwp on 2024/1/12.
//#include "myclass.h"void Adapter::request() {specificRequest();
}void Adaptee::specificRequest() {std::cout << "Adaptee被适配" << std::endl;
}

main.cpp

#include <iostream>
#include <mutex>
#include "myclass.h"int main() {Target *target = new Adapter();target->request();delete target;return 0;
}

双向适配器

myclass.h

//
// Created by yuwp on 2024/1/12.
//#ifndef DESIGNPATTERNS_MYCLASS_H
#define DESIGNPATTERNS_MYCLASS_H#include <iostream>class Target {  // 目标类
public:void request();
};class Adaptee {     // 适配者类
public:void specificRequest();
};class Adapter { // 适配器类
public:Adapter(Target *target);Adapter(Adaptee *adaptee);void request();void specificRequest();private:Target *m_target;Adaptee *m_adaptee;
};#endif //DESIGNPATTERNS_MYCLASS_H

myclass.cpp

//
// Created by yuwp on 2024/1/12.
//#include "myclass.h"void Target::request() {std::cout << "Target被适配" << std::endl;
}Adapter::Adapter(Target *target) {m_target = target;
}Adapter::Adapter(Adaptee *adaptee) {m_adaptee = adaptee;
}void Adapter::request() {if (m_adaptee) {m_adaptee->specificRequest();}
}void Adapter::specificRequest() {if (m_target) {m_target->request();}
}void Adaptee::specificRequest() {std::cout << "Adaptee被适配" << std::endl;
}

main.cpp

#include <iostream>
#include <mutex>
#include "myclass.h"int main() {Target *target = new Target();Adaptee *adaptee = new Adaptee();Adapter *adapter = new Adapter(target);adapter->specificRequest();delete adapter;adapter = new Adapter(adaptee);adapter->request();delete adapter;delete adaptee;delete target;return 0;
}

缺省适配器模式

myclass.h

//
// Created by yuwp on 2024/1/12.
//#ifndef DESIGNPATTERNS_MYCLASS_H
#define DESIGNPATTERNS_MYCLASS_H#include <iostream>class ServiceInterface {    // 适配者接口
public:virtual void request() = 0;virtual void request2() = 0;virtual void request3() = 0;
};class AbstractService : public ServiceInterface {     // 缺省适配器类
public:virtual void request() override;virtual void request2() override;virtual void request3() override;
};class Adaptee {     // 适配者类
public:void specificRequest();
};class Adapter : public AbstractService { // 具体适配器类
public:Adapter(Adaptee *adaptee);void request() override;private:Adaptee *m_adaptee;
};#endif //DESIGNPATTERNS_MYCLASS_H

myclass.cpp

//
// Created by yuwp on 2024/1/12.
//#include "myclass.h"Adapter::Adapter(Adaptee *adaptee) {m_adaptee = adaptee;
}void Adapter::request() {if (m_adaptee) {m_adaptee->specificRequest();}
}void Adaptee::specificRequest() {std::cout << "Adaptee被适配" << std::endl;
}void AbstractService::request() {std::cout << "缺省函数request" << std::endl;
}void AbstractService::request2() {std::cout << "缺省函数request2" << std::endl;
}void AbstractService::request3() {std::cout << "缺省函数request3" << std::endl;
}

main.cpp

#include <iostream>
#include <mutex>
#include "myclass.h"int main() {Adaptee *adaptee = new Adaptee();Adapter *adapter = new Adapter(adaptee);adapter->request();adapter->request2();adapter->request3();delete adapter;delete adaptee;return 0;
}

总结

优点

1. 将目标类和适配者类解耦。通过引入一个适配器类来重用现有的适配者类，无须修改原有结构。

2. 增加了类的透明性和复用性。将具体的业务实现过程封装在适配者类中，对于客户端类而言是透明的，而且提高了适配者类的复用性，同一个适配者类可以在多个不同的系统中复用。

3. 灵活性和扩展性都非常好。通过使用配置文件，可以很方便地更换适配器，也可以在不修改原有代码的基础上增加新的适配器类，完全符合开闭原则。

缺点

1. 对于Java、C＃等不支持多重类继承的语言，一次最多只能适配一个适配者类，不能同时适配多个适配者。

2. 适配者类不能为最终类，例如在Java中不能为final类，C＃中不能为sealed类。

3. 在Java、C＃等语言中，类适配器模式中的目标抽象类只能为接口，不能为类，其使用有一定的局限性。

适用场景

1. 系统需要使用一些现有的类，而这些类的接口（例如方法名）不符合系统的需要，甚至没有这些类的源代码。

2. 想创建一个可以重复使用的类，用于与一些彼此之间没有太大关联的类，包括一些可能在将来引进的类一起工作。

练习

对象适配器模式

//
// Created by yuwp on 2024/1/12.
//#ifndef DESIGNPATTERNS_MYCLASS_H
#define DESIGNPATTERNS_MYCLASS_H#include <iostream>class Encryption {  // 目标类
public:virtual std::string encrypt(std::string data) = 0;
};class ThirdLib {     // 适配者类
public:std::string specificEncrypt(std::string data);std::string specificDecrypt(std::string data);
};class AdapterEncyption : public Encryption {    // 适配器类
public:AdapterEncyption(ThirdLib *thirdLib);~AdapterEncyption();std::string encrypt(std::string data) override;private:ThirdLib *m_thirdLib;
};#endif //DESIGNPATTERNS_MYCLASS_H

myclass.cpp

//
// Created by yuwp on 2024/1/12.
//#include "myclass.h"AdapterEncyption::AdapterEncyption(ThirdLib *thirdLib) {m_thirdLib = thirdLib;
}AdapterEncyption::~AdapterEncyption() {if (m_thirdLib) {delete m_thirdLib;}
}std::string AdapterEncyption::encrypt(std::string data) {if (m_thirdLib) {return m_thirdLib->specificEncrypt(data);}return data;
}std::string ThirdLib::specificEncrypt(std::string data) {return "加密后的" + data;
}std::string ThirdLib::specificDecrypt(std::string data) {return "解密后的" + data;
}

main.cpp

#include <iostream>
#include <mutex>
#include "myclass.h"int main() {ThirdLib *thirdLib = new ThirdLib();Encryption *encryption = new AdapterEncyption(thirdLib);std::string data = encryption->encrypt("口令");std::cout << data << std::endl;data = encryption->encrypt("邮箱");std::cout << data << std::endl;return 0;
}

类适配器模式

myclass.h

//
// Created by yuwp on 2024/1/12.
//#ifndef DESIGNPATTERNS_MYCLASS_H
#define DESIGNPATTERNS_MYCLASS_H#include <iostream>class Encryption {  // 目标类
public:virtual std::string encrypt(std::string data) = 0;
};class ThirdLib {     // 适配者类
public:std::string specificEncrypt(std::string data);std::string specificDecrypt(std::string data);
};class AdapterEncyption : public Encryption, public ThirdLib {    // 适配器类
public:AdapterEncyption();~AdapterEncyption();std::string encrypt(std::string data) override;
};#endif //DESIGNPATTERNS_MYCLASS_H

myclass.cpp

//
// Created by yuwp on 2024/1/12.
//#include "myclass.h"AdapterEncyption::AdapterEncyption() {}AdapterEncyption::~AdapterEncyption() {}std::string AdapterEncyption::encrypt(std::string data) {return specificEncrypt(data);
}std::string ThirdLib::specificEncrypt(std::string data) {return "加密后的" + data;
}std::string ThirdLib::specificDecrypt(std::string data) {return "解密后的" + data;
}

main.cpp

#include <iostream>
#include <mutex>
#include "myclass.h"int main() {Encryption *encryption = new AdapterEncyption();std::string data = encryption->encrypt("口令");std::cout << data << std::endl;data = encryption->encrypt("邮箱");std::cout << data << std::endl;delete encryption;return 0;
}