设计模式——模板方法模式

模板方法模式

模板方法模式是一种行为设计模式，在超类中定义一个算法的框架，允许子类在不修改结构的情况下重写算法的特定步骤。

继承的实现应该让重复代码尽可能上升到父类去，而不是每个子类都去重复实现
当我们要完成在某一细节层次一致的一个过程或者一系列步骤时，但是其个别步骤在更详细的层次上的实现可能不同时，我们通常考虑用模板方法来处理。

#include <iostream>
#include <string>// 模板方法模式
using std::cout;// 抽象类定义了一个模板方法，其中包含一些算法的骨架
// 在具体的子类去实现这些细节class AbstrateClass
{
public:void TemplateMethod() const{this->BaseOperation1();this->RequireOperation1();this->BaseOperation2();this->Hook1();this->RequireOperation2();this->BaseOperation3();this->Hook2();}// 已经实现的操作
protected:void BaseOperation1() const{cout << "AbstrateClass says: I am doing the bulk of the work\n";}void BaseOperation2() const{cout << "AbstrateClass says: But I let subclasses override some operations\n";}void BaseOperation3() const{cout << "AbstrateClass says: But I am doing the bulk of the work anyway\n";}// 子类必须实现的操作virtual void RequireOperation1() const = 0;virtual void RequireOperation2() const = 0;// 俗称钩子 hooks，子类可以实现也可以不实现， 这些钩子在程序中提供了大量的扩展点virtual void Hook1() const {}virtual void Hook2() const {}
};// 具体类中必须实现基类的所有抽象操作(纯虚函数)，可以选择性地使用默认实现覆盖某些操作
class ConcreteClass1 : public AbstrateClass
{
protected:void RequireOperation1() const override{cout << "ConcreteClass1 says: Implemented Operation1\n";}void RequireOperation2() const override{cout << "ConcreteClass1 says: Implememted Operation2\n ";}
};// 通常具体类只覆盖基类的一小部分操作
class ConcreteClass2 : public AbstrateClass
{
protected:void RequireOperation1() const override{cout << "ConcreteClass2 says: Implemented Operation1\n";}void RequireOperation2() const override{cout << "ConcreteClass2 says: Implememted Operation2\n ";}void Hook1() const override{cout << "ConcreteClass2 says: Overridden Hook1\n";}
};// 客户端代码调用模板方法，不必知道它所操作对象的具体类，只要通过基类提供的接口与对象交互即可
void ClientCode(AbstrateClass *class_)
{class_->TemplateMethod();
}int main()
{std::cout << "Same client code can work with different subclasses:\n";ConcreteClass1 *concreteClass1 = new ConcreteClass1;ClientCode(concreteClass1);std::cout << "\n";std::cout << "Same client code can work with different subclasses:\n";ConcreteClass2 *concreteClass2 = new ConcreteClass2;ClientCode(concreteClass2);delete concreteClass1;delete concreteClass2;return 0;
}

`
Same client code can work with different subclasses:
AbstrateClass says: I am doing the bulk of the work
ConcreteClass1 says: Implemented Operation1
AbstrateClass says: But I let subclasses override some operations
ConcreteClass1 says: Implememted Operation2
AbstrateClass says: But I am doing the bulk of the work anyway

Same client code can work with different subclasses:
AbstrateClass says: I am doing the bulk of the work
ConcreteClass2 says: Implemented Operation1
AbstrateClass says: But I let subclasses override some operations
ConcreteClass2 says: Overridden Hook1
ConcreteClass2 says: Implememted Operation2
AbstrateClass says: But I am doing the bulk of the work anyway
`