设计模式之- 策略模式（Strategy Pattern）

#include<iostream>

using namespace std;


class Strategy {
public:
    virtual int doOperation(int num1, int num2) = 0;
};


class OperationAdd :public Strategy{
public:
    int doOperation(int num1, int num2) {
       return num1 + num2;
    }
};




class OperationSubstract  :public Strategy{
public:
    int doOperation (int num1, int num2) {
       return num1 - num2;
    }
};



class OperationMultiply   :public Strategy{
public:
    int doOperation(int num1, int num2) {
       return num1 * num2;
    }
};



class Context {
    Strategy* strategy;
public:
    Context(Strategy* strategy){
        this->strategy = strategy;
    }

    void setStrategy(Strategy* st){
        if(this->strategy != nullptr)  delete this->strategy;//注意析构
        this->strategy = st;
    }

    int executeStrategy(int num1, int num2){
        return strategy->doOperation(num1, num2);
    }
};


class StrategyPatternDemo {
public:
    static void method() {
        Context* context = new Context(new OperationAdd());    
        cout<<"10 + 5 = " << context->executeStrategy(10, 5)<<endl;

        context->setStrategy(new OperationSubstract());      
        cout<<"10 - 5 = " << context->executeStrategy(10, 5)<<endl;

        context->setStrategy(new OperationMultiply());    
        cout<<"10 * 5 = " << context->executeStrategy(10, 5)<<endl;
    }
};


int main(int argc,char** argv){
    StrategyPatternDemo::method();
}