战略和Flyweight模式

Question

我已经读过"策略对象经常做出好的飞重"(来自可重复使用的面向对象软件的设计模式元素),我想知道如何实现它.我没有在互联网上找到任何例子.

遵循这个想法,代码(C#)是否正确？

谢谢!

using System;
using System.Collections.Generic;

namespace StrategyFlyweight
{
    class Program
    {
        static void Main(string[] args)
        {
            Client client = new Client();
            for(int i = 1; i <= 10;i++)
            {
                client.Execute(i);
            }
            Console.ReadKey();
        }
    }

    public interface IStrategy
    {
        void Check(int number);
    }

    public class ConcreteStrategyEven : IStrategy
    {
        public void Check(int number)
        {
            Console.WriteLine("{0} is an even number...", number);
        }
    }

    public class ConcreteStrategyOdd : IStrategy
    {
        public void Check(int number)
        {
            Console.WriteLine("{0} is an odd number...", number);
        }
    }

    public class FlyweightFactory
    {
        private Dictionary<string, IStrategy> _sharedObjects = new Dictionary<string, IStrategy>();

        public IStrategy GetObject(int param)
        {
            string key = (param % 2 == 0) ? "even" : "odd";

            if (_sharedObjects.ContainsKey(key))
                return _sharedObjects[key];
            else
            {
                IStrategy strategy = null;
                switch (key)
                {
                    case "even":
                        strategy = new ConcreteStrategyEven();
                        break;
                    case "odd":
                        strategy = new ConcreteStrategyOdd();
                        break;
                }
                _sharedObjects.Add(key, strategy);
                return strategy;
            }
        }
    }

    public class Client
    {
        private IStrategy _strategy;
        private FlyweightFactory _flyweightFactory = new FlyweightFactory();

        public void Execute(int param)
        {
            ChangeStrategy(param);
            _strategy.Check(param);
        }

        private void ChangeStrategy(int param)
        {
            _strategy = _flyweightFactory.GetObject(param);
        }
    }
}

Answer 1

我认为,要在此处正确实现flyweight模式,您的工厂方法应始终返回特定策略的相同实例(如ConcreteStrategyEven),而不是每次都构造一个新实例.

如果我没有弄错,那么说Strategy对象制作好的Flyweights就是它们通常不封装任何状态(因为它们代表算法而不是实体)并且可以重复使用.

以下是Flyweight工厂示例的链接:http: //www.java2s.com/Code/Java/Design-Pattern/FlyweightFactory.htm.请注意这一部分,特别是:

  public synchronized FlyweightIntr getFlyweight(String divisionName) {
    if (lstFlyweight.get(divisionName) == null) {
      FlyweightIntr fw = new Flyweight(divisionName);
      lstFlyweight.put(divisionName, fw);
      return fw;
    } else {
      return (FlyweightIntr) lstFlyweight.get(divisionName);
    }
  }

在工厂方法中,FlyweightIntr只有在没有正确的新方法时才初始化new ; 否则从中检索lstFlyweight.