設計模式（一）————策略模式（Strategy Pattern）

定義：封裝一組算法，讓算法之間可以相互替換

類圖：

 

C++實現：

#include<iostream>
using namespace std;

class IStrategy 
{
public:
	virtual void AlgorithmInterface() = 0;
};
class StrategyA :public IStrategy
{
public :
	virtual void AlgorithmInterface()
	{
		cout << "A" << endl;
	}
	~StrategyA() {};
};
class StrategyB :public IStrategy
{
public:
	virtual void AlgorithmInterface()
	{
		cout << "B" << endl;
	}
	~StrategyB() {};
};
class StrategyC :public IStrategy
{
public:
	virtual void AlgorithmInterface()
	{
		cout << "C" << endl;
	}
	~StrategyC() {};
};
class Context
{
	IStrategy* strategy;
public:
	Context(IStrategy* strategy)
	{
		this->strategy = strategy;
	}
	void execute()
	{
		strategy->AlgorithmInterface();
	}
};
int main()
{
	IStrategy* strategy;
	StrategyA strategyA;
	StrategyB strategyB;
	StrategyC strategyC;

	strategy = &strategyA;
	Context context1(strategy);
	context1.execute();

	strategy = &strategyB;
	Context context2(strategy);
	context2.execute();

	strategy = &strategyC;
	Context context3(strategy);
	context3.execute();
	return 0;
}

C#實現：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{

    interface IStrategy
    {
        void AlgorithmInterface();
    }
    class StrategyA :IStrategy
    {
        public void AlgorithmInterface()
        {
            Console.WriteLine("A");   
        }
    }
    class StrategyB : IStrategy
    {
        public void AlgorithmInterface()
        {
            Console.WriteLine("B");
        }
    }
    class StrategyC : IStrategy
    {
        public void AlgorithmInterface()
        {
            Console.WriteLine("C");
        }
    }
    class Context
    {
        private IStrategy strategy;
        public Context(IStrategy strategy)
        {
            this.strategy = strategy;
        }
        public void execute()
        {
            strategy.AlgorithmInterface();
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            StrategyA strategyA = new StrategyA();
            StrategyB strategyB = new StrategyB();
            StrategyC strategyC = new StrategyC();

            Context context = new Context(strategyA);
            context.execute();

            context = new Context(strategyB);
            context.execute();

            context = new Context(strategyC);
            context.execute();
        }
    }
}