元哥的筆記

何時使用

• 系統中有大量物件時
• 這些物件消耗大量內存時
• 這些物件的狀態大部分可以外部化時

 優點：大大減少了物件的創建，降低了程序內存的占用，提高效率
 缺點：提高了系統的複雜度。需要分離出內部狀態和外部狀態，而外部狀態具有固化特性，不應該隨著內部狀態的改變而改變

使用場景

1. 系統存在大量相似物件
2. 需要緩衝的場景

    class Program
    {
        static void Main(string[] args)
        {
            int extrinsicstate = 22;
            FlyweightFactory f = new FlyweightFactory();

            Flyweight fx = f.GetFlyweight("X");
            fx.Operation(--extrinsicstate);

            Flyweight fy = f.GetFlyweight("Y");
            fy.Operation(--extrinsicstate);

            Flyweight fz = f.GetFlyweight("Z");
            fz.Operation(--extrinsicstate);

            UnsharedConcreteFlyweight uf = new UnsharedConcreteFlyweight();
            uf.Operation(--extrinsicstate);

            Console.Read();


        }
    }

    class FlyweightFactory
    {
        private Hashtable flyweights = new Hashtable();

        public FlyweightFactory()
        {
            flyweights.Add("X",new ConcreteFlyweight());
            flyweights.Add("Y", new ConcreteFlyweight());
            flyweights.Add("Z", new ConcreteFlyweight());
        }

        public Flyweight GetFlyweight(string key)
        {
            return ((Flyweight) flyweights[key]);
        }
    }

    abstract class Flyweight
    {
        public abstract void Operation(int extrinsicstate);
    }

    class ConcreteFlyweight:Flyweight
    {
        public override void Operation(int extrinsicstate)
        {
            Console.WriteLine($"具體Flyweight:{extrinsicstate}");
        }
    }
    class UnsharedConcreteFlyweight : Flyweight
    {
        public override void Operation(int extrinsicstate)
        {
            Console.WriteLine($"不共用的具體Flyweight:{extrinsicstate}");
        }
    }

 

元哥的筆記