DesignPatterns_Adapter_adapter头像-优快云博客

本文介绍了适配器模式的基本概念及其实现方式，探讨了如何通过接口适配使不兼容接口的类协同工作，并对比了类适配器与对象适配器的不同之处。

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////////////////////////////////////////////////////////////////////////////////
// Adapter pattern
// - Convert the interface of a class into another interface clients expect.
//   Adapters lets classes work together that couldn't otherwise because of
//   incompatible interfaces.
// - Interface adaptation lets us incorporate our class into existing systems
//   that might expect different interfaces to the class.
//
// Author  : ZAsia
// Data    : 15/05/07
// Warning : In practice, declaration and implementation should be 
//           separated(in .h and .cpp).
////////////////////////////////////////////////////////////////////////////////

#include 
using namespace std;

#undef CLASS_ADAPTER

// Target
// - defines the domain-specific interface that Client uses.
class Target
{
public:
	virtual void Request() { cout << "Target::Request" << endl; }
};

// Adaptee
// - defines an existing interface that needs adapting.
class Adaptee
{
public:
	void SpecificRequest() { cout << "Adaptee::SpecificRequest" << endl; }
};

// Adapter
// - adapts the interface of Adaptee to the Target interface.
#ifdef CLASS_ADAPTER
// 1. A class adapter uses multiple inheritance to adapt one interface to another.
class Adapter : public Target, private Adaptee
{
public:
	virtual void Request() { Adaptee::SpecificRequest(); }
};
#else
// 2. A object adapter relies on object composition.
class Adapter : public Target
{
public:
	Adapter() : m_pAdaptee(new Adaptee) { }

	~Adapter()
	{
		if (m_pAdaptee != nullptr) 
		{
			delete m_pAdaptee;
			m_pAdaptee = nullptr;
		}
	}

	virtual void Request()
	{
		m_pAdaptee->SpecificRequest();
	}

private:
	Adaptee *m_pAdaptee;
};
#endif

// Client
// - collaborates with objects conforming to the Target interface
//
// Collaborations
// - Clients call operations on an Adapter instance. In turn, the adapter
//   calls Adaptee operations that carry out the request.
int main()
{
	Target *pTargetObj = new Adapter();
	pTargetObj->Request();

	if (pTargetObj != nullptr)
	{
		delete pTargetObj;
		pTargetObj = nullptr;
	}

	return 0;
}

/////////////////////////////////////////////////////////////////////////
// 1. The amount of work Adapter does depends on how similar the Target
//    interface is to Adaptee's.
// 2. A class adapter uses multiple inheritance to adapt interfaces. The 
//    key to class adapters is to use one inheritance branch to inherit the
//    interface and another branch to inherit the implementation. The usual
//    way to make this distinction in C++ is to inherit the interface publicly
//    and inherit the implementation privately.
// 3. The object adapter uses object composition to combine classes with
//    different interfaces.