享元（Flyweight）模式的定义：运用共享技术来有効地支持大量细粒度对象的复用。
享元模式的主要优点是：相同对象只要保存一份，这降低了系统中对象的数量，从而降低了系统中细粒度对象给内存带来的压力。
其主要缺点是：
为了使对象可以共享，需要将一些不能共享的状态外部化，这将增加程序的复杂性。
读取享元模式的外部状态会使得运行时间稍微变长。
/**
* 抽象享元角色（Flyweight）:是所有的具体享元类的基类，为具体享元规范需要实现的公共接口，非享元的外部状态以参数的形式通过方法传入。
* 具体享元（Concrete Flyweight）角色：实现抽象享元角色中所规定的接口。
* 非享元（Unsharable Flyweight)角色：是不可以共享的外部状态，它以参数的形式注入具体享元的相关方法中。
* 享元工厂（Flyweight Factory）角色：负责创建和管理享元角色。当客户对象请求一个享元对象时，享元工厂检査系统中是否存在符合要求的享元对象，如果存在则提供给客户；如果不存在的话，则创建一个新的享元对象。
**/
public class FlyweightPattern {
public static void main(String[] args) {
FlyweightFactory factory=new FlyweightFactory();
Flyweight f01=factory.getFlyweight("a");
Flyweight f02=factory.getFlyweight("a");
Flyweight f03=factory.getFlyweight("a");
Flyweight f11=factory.getFlyweight("b");
Flyweight f12=factory.getFlyweight("b");
f01.operation(new UnsharedConcreteFlyweight("第1次调用a。"));
f02.operation(new UnsharedConcreteFlyweight("第2次调用a。"));
f03.operation(new UnsharedConcreteFlyweight("第3次调用a。"));
f11.operation(new UnsharedConcreteFlyweight("第1次调用b。"));
f12.operation(new UnsharedConcreteFlyweight("第2次调用b。"));
}
}
/**
* 非享元角色
**/
class UnsharedConcreteFlyweight {
private String info;
public UnsharedConcreteFlyweight (String info) {
this.info = info;
}
public String getInfo() {
return this.info;
}
public void setInfo(String info) {
this.info = info;
}
}
/**
* 抽象享元角色
**/
interface Flyweight {
public void operation(UnsharedConcreteFlyweight state);
}
/**
* 具体享元角色
**/
class ConcreteFlyweight implements Flyweight {
private String key;
ConcreteFlyweight(String key) {
this.key = key;
System.out.println("具体享元"+key+"被创建！");
}
public void operation(UnsharedConcreteFlyweight outState) {
System.out.print("具体享元"+key+"被调用，");
System.out.println("非享元信息是:"+outState.getInfo());
}
}
/**
* 享元工厂角色
**/
class FlyweightFactory {
private HashMap<String, Flyweight> flyweights = new HashMap<String, Flyweight>();
public Flyweight getFlyweight(String key) {
Flyweight flyweight = (Flyweight)flyweights.get(key);
if (flyweight != null) {
System.out.println("具体享元"+key+"已经存在，被成功获取！");
} else {
flyweight = new ConcreteFlyweight(key);
flyweights.put(key, flyweight);
}
return flyweight;
}
}
