策略模式(Strategy):它定义了算法家族,分别封装起来,让他们之间可以互相替换,此模式让算法的变化,不会影响到使用算法的客户。
context,用一个ConcreteStrategy来配置,维护一个对Strategy对象的引用。
策略模式和工厂模式的不同之处:
工厂来生成算法对象,这没有错,但算法只是一种策略,最重要的是这些算法是随时间都可能互相替换的,这就是变化点,而封装变化就是面向对象的一个重要的思维方式,
策略模式结构图如下所示:
来举一个栗子:
程序运行截图如下;
源码如下:
strategy.h
#pragma once
#include <iostream>
using namespace std;
class Strategy{
public:
virtual void algorithmInterface() = 0;
virtual ~Strategy(){
cout << "~Strategy() called!" << endl;
}
};
class ConcreteStrategyA: public Strategy{
public:
void algorithmInterface(){
cout << "arithmetic A is called!" << endl;
}
~ConcreteStrategyA(){
cout << "~ConcreteStrategyA() called!" << endl;
}
};
class ConcreteStrategyB: public Strategy{
public:
void algorithmInterface(){
cout << "arithmetic A is called!" << endl;
}
~ConcreteStrategyB(){
cout << "~ConcreteStrategyB() called!" << endl;
}
};
class ConcreteStrategyC: public Strategy{
public:
void algorithmInterface(){
cout << "arithmetic C is called!" << endl;
}
~ConcreteStrategyC(){
cout << "~ConcreteStrategyC() called!" << endl;
}
};
class Context{
public:
Context(Strategy *strategy){
m_strategy = strategy;
}
~Context(){
delete m_strategy;
}
void contextInterface(){
m_strategy->algorithmInterface();
}
private:
Strategy *m_strategy;
};
main.cpp
#include "strategy.h"
int main(){
Context *contextA, *contextB, *contextC;
//由于实例化不同的策略,所以最终在调用context->contextInterface()时,所获得的结果就不尽相同
contextA = new Context(new ConcreteStrategyA);
contextA->contextInterface();
delete contextA;
cout << endl << "----------**********----------" << endl;
contextB = new Context(new ConcreteStrategyB);
contextB->contextInterface();
delete contextB;
cout << endl << "----------**********----------" << endl;
contextC = new Context(new ConcreteStrategyC);
contextC->contextInterface();
delete contextC;
getchar();
return 0;
}
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