# 享元模式

属于结构型模式。
运用共享技术有效地支持大量细粒度的对象。

享元模式可以避免大量非常相似类的开销。如果能把那些不同的参数移到类实例的外面，在方法调用时将他们传递进来，就可以通过共享大幅度减少单个实例的数目。

在 CSharp 中，string 就是运用了享元模式。例：声明两个字符串 string A = "A"; string B = "A"; 使用 Object.ReferenceEquals (A, B); 检查 A 和 B 是否是相同的实例，结果：true

# 类图

	namespace StructuralPattern_FlyweightPattern
	{
	/// <summary>
	/// 颜色
	/// </summary>
	public class Color
	{
	public string ColorName;

	public Color(string colorName)
	{
	ColorName = colorName;
	}
	}
	}

	namespace StructuralPattern_FlyweightPattern
	{
	/// <summary>
	/// 形状
	/// </summary>
	public abstract class Shape
	{
	public Color MyColor;

	/// <summary>
	/// 形状
	/// </summary>
	public abstract void MyShape();
	}
	}

	namespace StructuralPattern_FlyweightPattern
	{
	/// <summary>
	/// 正方形
	/// </summary>
	public class Square : Shape
	{
	public override void MyShape()
	{
	Console.WriteLine("Shape: Square\nColor: " + MyColor.ColorName);
	}
	}
	}

	namespace StructuralPattern_FlyweightPattern
	{
	public class FlyweightFactory
	{
	private Dictionary<string, Shape> ShapeDic;

	public FlyweightFactory()
	{
	ShapeDic = new Dictionary<string, Shape>();
	}

	/// <summary>
	/// 获取 Shape 类的实例
	/// </summary>
	/// <typeparam name="T"></typeparam>
	/// <param name="name"></param>
	/// <returns></returns>
	public Shape GetShape<T>(string name) where T : Shape
	{
	if (ShapeDic.ContainsKey(name))
	{
	return ShapeDic[name];
	}
	else
	{
	T temp = Activator.CreateInstance(typeof(T)) as T;
	ShapeDic.Add(name, temp);
	return temp;
	}
	}
	}
	}

	namespace StructuralPattern_FlyweightPattern
	{
	public class Program
	{
	private static void Main()
	{
	FlyweightFactory factory = new FlyweightFactory();

	Shape shape_0 = factory.GetShape<Square>("Square");
	shape_0.MyColor = new Color("Red");

	shape_0.MyShape();
	Console.WriteLine();

	// 此时，shape_0 和 shape_1 是同一个实例
	Shape shape_1 = factory.GetShape<Square>("Square");
	shape_1.MyColor = new Color("Blue");

	shape_1.MyShape();
	}
	}
	}

运行结果：
Shape: Square
Color: Red

Shape: Square
Color: Blue