C# 设计模式（12）享元模式

享元模式

1.解决对象复用问题

2.不破坏原本类的封装

3.池化资源管理：避免对象重复创建和销毁（尤其是非托管资源）

4.字符串 内存分配使用是享元模式（排除部分分配）

代码实现：

namespace FlyWeightPattern
{
    public interface ILetter
    {
       public string GetLetter();
    }
    class LetterA:ILetter
    {
        private string name = "A";
        public LetterA()
        {
            Console.WriteLine($"Letter {name} has been Created");
        }
        public string GetLetter()
        {
            return name;
        }
    }
    class LetterE:ILetter
    {
        private string name = "E";
        public LetterE()
        {
            Console.WriteLine($"Letter {name} has been Created");
        }
        public string GetLetter()
        {
            return name;
        }
    }
    class LetterN:ILetter
    {
        private string name = "N";
        public LetterN()
        {
            Console.WriteLine($"Letter {name} has been Created");
        }
        public string GetLetter()
        {
            return name;
        }
    }
    class LetterP:ILetter
    {
        private string name = "P";
        public LetterP()
        {
            Console.WriteLine($"Letter {name} has been Created");
        }
        public string GetLetter()
        {
            return name;
        }
    }
    class LetterR:ILetter
    {
        private string name = "R";
        public LetterR()
        {
            Console.WriteLine($"Letter {name} has been Created");
        }
        public string GetLetter()
        {
            return name;
        }
    }
        private string name = "T";
        public LetterT()
        {
            Console.WriteLine($"Letter {name} has been Created");
        }
        public string GetLetter()
        {
            return name;
        }
}

享元封装：

    public class FlyWeight
    {
        private  static Dictionary<LetterType, ILetter> _letterDictionary = new Dictionary<LetterType, ILetter>();
        private  static object _flyWeightLock = new object();

        public static ILetter CreateWordPattern(LetterType letterType)
        {
            if (!_letterDictionary.ContainsKey(letterType))
            {
                lock (_flyWeightLock)
                {
                    if (!_letterDictionary.ContainsKey(letterType))
                    {
                        switch (letterType)
                        {
                            case LetterType.A:
                                _letterDictionary.Add(letterType, new LetterA());
                                break;
                            case LetterType.P:
                                _letterDictionary.Add(letterType, new LetterP());
                                break;
                            case LetterType.T:
                                _letterDictionary.Add(letterType, new LetterT());
                                break;
                            case LetterType.E:
                                _letterDictionary.Add(letterType, new LetterE());
                                break;
                            case LetterType.R:
                                _letterDictionary.Add(letterType, new LetterR());
                                break;
                            case LetterType.N:
                                _letterDictionary.Add(letterType, new LetterN());
                                break;
                            default:
                                throw new ArgumentOutOfRangeException(nameof(letterType), letterType, null);
                        }
                    }
                }
            }
            return _letterDictionary[letterType];
        }

        public enum LetterType
        {
            P,
            A,
            T,
            E,
            R,
            N
        }
    }

代码调用：

    class Program
    {
        static void Main(string[] args)
        {
            Task.Run(() =>
            {
                for (int i = 0; i < 3; i++)
                {
                    ILetter letter_P = FlyWeight.CreateWordPattern(FlyWeight.LetterType.P);
                    ILetter letter_A = FlyWeight.CreateWordPattern(FlyWeight.LetterType.A);
                    ILetter letter_T = FlyWeight.CreateWordPattern(FlyWeight.LetterType.T);
                    ILetter letter_E = FlyWeight.CreateWordPattern(FlyWeight.LetterType.E);
                    ILetter letter_R = FlyWeight.CreateWordPattern(FlyWeight.LetterType.R);
                    ILetter letter_N = FlyWeight.CreateWordPattern(FlyWeight.LetterType.N);

                    Console.WriteLine(
                        $"{letter_P.GetLetter().ToUpper()}{letter_A.GetLetter().ToLower()}{letter_T.GetLetter().ToLower()}{letter_T.GetLetter().ToLower()}{letter_E.GetLetter().ToLower()}{letter_R.GetLetter().ToLower()}{letter_N.GetLetter().ToLower()}"
                    );
                }
            });
            Console.ReadLine();
        }
    }

结果：