两种语言实现设计模式（C++和Java）（三：策略模式）

策略模式是指定义一系列的算法，把它们一个个封装起来，并且使它们可相互替换。本模式使得算法可独立于使用它的客户而变化。也就是说这些算法所完成的功能一样，对外的接口一样，只是各自实现上存在差异。用策略模式来封装算法，效果比较好。

本文以自己实际项目中策略模式的实际应用为例：实现无人驾驶车辆的定位有两种方式：GNSS（带差分信号的GPS）和SLAM，实现两种方法的定位可以视为采用两种不同的策略。定义抽象类locateStratey，再通过委托的方式将具体的算法实现委托给具体的Strategy类来实现。

Context委托类是Strategy模式的关键，*Strategy通过“组合”（委托）方式实现算法（实现）的异构，

一、C++代码

 #include <iostream>

 using namespace std;

 //Suppose the position is 1 when strategy is Gnss ,and 2 when strategy is slam

 class LocateStrategy{

 public:

     LocateStrategy(){}

     ~LocateStrategy(){}

     virtual int locateAlgorithm()=;

 };

 class StrategyGnss:public LocateStrategy

 {

 public:

     StrategyGnss() {}

     ~StrategyGnss() {}

     int locateAlgorithm(){

         cout << "Locate By GNSS" << endl;

         return ;

     }

 };

 class StrategySlam:public LocateStrategy

 {

 public:

     StrategySlam() {}

     ~StrategySlam() {}

     int locateAlgorithm(){

         cout << "Locate By SLAM" << endl;

         return ;

     }

 };

 class Context

 {

 public:

     Context(LocateStrategy* strategy) {

         _strategy = strategy;

     }

     ~Context(){

         delete _strategy;

     }

     int locateCalculate(){

        return this->_strategy->locateAlgorithm();

     }

 private:

     LocateStrategy* _strategy;

 };

 int main()

 {

     LocateStrategy *pStrategy = new StrategyGnss();

     Context *pCon = new Context(pStrategy);

     cout <<pCon->locateCalculate() << endl;

     //Strategy Replacement

     pStrategy = new StrategySlam();

     pCon = new Context(pStrategy);

     cout <<pCon->locateCalculate() << endl;

 }

输出:

Locate By GNSS

Locate By SLAM

二、Java代码

 public interface ILocateStrategy {

     int locateAlgorithm();

 }

 public class StrategyGnss implements ILocateStrategy{

     public int locateAlgorithm() {

         System.out.println("locate calculate by Gnss");

         return 1;

     }

 }

 public class StrategySlam implements ILocateStrategy {

     public int locateAlgorithm() {

         System.out.println("locate calculate by Slam");

         return 2;

     }

 }

 public class Context {

     private ILocateStrategy strategy;

     public Context(ILocateStrategy strategy){

         this.strategy = strategy;

     }

     public int getPosition(){

         return  strategy.locateAlgorithm();

     }

 }

 public class Main {

     public static void main(String[] args){

         Context context = new Context(new StrategyGnss());

         System.out.println(context.getPosition());

         context = new Context(new StrategySlam());

         System.out.println(context.getPosition());

     }

 }

输出：

locate calculate by Gnss
1
locate calculate by Slam
2

巴特西

两种语言实现设计模式（C++和Java）（三：策略模式）

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