享元模式

享元模式（Flyweight）运用共享技术有效地支持大量细粒度的对象

使用场景：

如果一个应用程序使用了大量的对象，而大量的对象造成了很大的存储开销时就应该考虑使用；还有就是对象的
大多数状态可以外部状态，如果删除对象的外部状态，那么就可以用相对较少的共享对象取代很多组对象，
此时就可以考虑享元模式

使用好处：

享元模式可以避免大量非常类似的开销。再程序设计中，有时需要生成大量细粒度的类实例来表示数据。
如果发现这些实列除了几个参数外基本上都相同，有时就能够大幅度的减少需要实例化的类的数量。如果
把这些参数移到类实例的外面，在方法调用时将它们传递进来，就可以通过共享大幅度的减少单个实例的个数。

实现代码如下：

1 public abstract class Flyweight {
2     public abstract void operation(int extrinsicstate);
3 }

Flyweight

1 public class ConcreteFlyweight extends Flyweight{
2 
3     @Override
4     public void operation(int extrinsicstate) {
5         System.out.println("具体实现Flyweight--》"+extrinsicstate);
6         
7     }
8 
9 }

ConcreteFlyweight

1 public class UnSharedConcreteFlyweight extends Flyweight{
2 
3     @Override
4     public void operation(int extrinsicstate) {
5         System.out.println("不共享具体实现Flyweight--》"+extrinsicstate);
6         
7     }
8 
9 }

UnSharedConcreteFlyweight

 1 import com.sun.org.apache.xalan.internal.xsltc.runtime.Hashtable;
 2 
 3 public class FlyweightFactory {
 4     private Hashtable flyweights = new Hashtable();
 5 
 6     public FlyweightFactory() {
 7         flyweights.put("x", new ConcreteFlyweight());
 8         flyweights.put("y", new ConcreteFlyweight());
 9         flyweights.put("z", new ConcreteFlyweight());
10     }
11     
12     public Flyweight getFlyweight(String key){
13         return (Flyweight) flyweights.get(key);
14     }
15     
16 }

FlyweightFactory

 1 public  class FlyweightTest {
 2     public static void main(String[] args) {
 3         int extrinsicstate = 22;
 4         FlyweightFactory f = new FlyweightFactory();
 5          
 6         ConcreteFlyweight fx = (ConcreteFlyweight) f.getFlyweight("x");
 7         fx.operation(--extrinsicstate);
 8         
 9         ConcreteFlyweight fy = (ConcreteFlyweight) f.getFlyweight("y");
10         fy.operation(--extrinsicstate);
11         
12         ConcreteFlyweight fz = (ConcreteFlyweight) f.getFlyweight("z");
13         fz.operation(--extrinsicstate);
14         
15         UnSharedConcreteFlyweight uf = new UnSharedConcreteFlyweight();
16         uf.operation(--extrinsicstate);
17     }
18 }

test

具体实现Flyweight--》21
具体实现Flyweight--》20
具体实现Flyweight--》19
不共享具体实现Flyweight--》18

测试打印