结构

享元模式

说明

Use sharing to support large numbers of similar objects efficiently.

通过共享以便有效的支持大量小颗粒对象。

适用条件

  1. 一个程序使用了大量的对象;
  2. 完全由于使用大量的对象, 造成了很大的存储开销;
  3. 对象的大多数状态都可以变为外部状态;
  4. 如果删除对象的外部状态, 那么可以使用相对较少的共享对象取代很多组对象;
  5. 应用程序不依赖于对象标识, 由于享元对象可以被共享, 所以概念上明显有别的对象, 标识测试将返回真值;

实现

public interface ICoffeeOrder {

   void ServeCoffee(CoffeeOrderContext context);

}

public class CoffeeFlavor : ICoffeeOrder {

   public string Flavor {
      get;
      private set;
   }

   public CoffeeFlavor(string newFlavor) {
      this.Flavor = newFlavor;
   }

   public void ServeCoffee(CoffeeOrderContext context) {
      Console.WriteLine("Serving coffee flavor {0} to table     {1} .", this.Flavor, context.Table);
   }

}

public class CoffeeOrderContext {

   public int Table {
      get;
      private set;
   }

   public CoffeeOrderContext(int tableNumber) {
      this.Table = tableNumber;
   }

}

public class CoffeeFlavorFactory {

   private readonly IDictionary<string, CoffeeFlavor> _flavors     = new Dictionary<string, CoffeeFlavor>();

   public CoffeeFlavor GetCoffeeFlavor(string flavorName) {
      CoffeeFlavor flavor;
      if (this._flavors.TryGetValue(flavorName, out flavor)) {
         return flavor;
      }
      flavor = new CoffeeFlavor(flavorName);
      this._flavors.Add(flavorName, flavor);
      return flavor;
   }

   public int TotalFlaversMade {
      get {
         return this._flavors.Count;
      }
   }

}

class Program {

   private static CoffeeFlavor[] _flavors = new     CoffeeFlavor[100];
   private static CoffeeOrderContext[] _tables = new     CoffeeOrderContext[100];
   private static int _ordersMade;
   private static CoffeeFlavorFactory _factory;

   private static void TakeOrder(string flaver, int table) {
      _flavors[_ordersMade] = _factory.GetCoffeeFlavor(flaver);
      _tables[_ordersMade++] = new CoffeeOrderContext(table);
   }

   static void Main(string[] args) {
      _factory = new CoffeeFlavorFactory();

      TakeOrder("Cappuccino", 2);
      TakeOrder("Cappuccino", 2);
      TakeOrder("Frappe", 1);
      TakeOrder("Frappe", 1);
      TakeOrder("Xpresso", 1);
      TakeOrder("Frappe", 897);
      TakeOrder("Cappuccino", 97);
      TakeOrder("Cappuccino", 97);
      TakeOrder("Frappe", 3);
      TakeOrder("Xpresso", 3);
      TakeOrder("Cappuccino", 3);
      TakeOrder("Xpresso", 96);
      TakeOrder("Frappe", 552);
      TakeOrder("Cappuccino", 121);
      TakeOrder("Xpresso", 121);

      for (int i = 0; i < _ordersMade; i++) {
         _flavors[i].ServeCoffee(_tables[i]);
      }

      Console.WriteLine();
      Console.WriteLine("Total CoffeeFlavor objects made {0}",     _factory.TotalFlaversMade);
      Console.ReadKey();
   }
}