享元模式

定义：使用共享对象可以有效的支持大量的细粒度的对象

FlyWeight抽象享元类：通常是一个接口或抽象类，声明公共方法，这些方法可以向外界提供对象的内部状态，设置外部状态。
UnsharedConcreteFlyWeight非共享享元类：不能被共享的子类可以设计为非共享享元类。
ConcreteFlyWeight具体享元类：为内部状态提供成员变量进行存储。
FlyWeightFactory享元工厂类：创建并管理享元对象，享元池一般设计为键值对。

//抽象享元类abstract class Flyweight {    private String intrinsic;    protected final String Extrinsic;    public Flyweight(String Extrinsic){        this.Extrinsic = Extrinsic;    }    public abstract void operate();    public String getIntrinsic(){        return intrinsic;    }    public void setIntrinsic(String intrinsic){        this.intrinsic = intrinsic;    }}//具体享元类class ConcreteFlyweight1 extends Flyweight{    public ConcreteFlyweight1(String Extrinsic) {        super(Extrinsic);    }    @Override    public void operate() {    }}//享元工厂class FlyweightFactory {    //对象池    private static HashMap<String,Flyweight> pool = new HashMap<>();    public static Flyweight getFlyweight(String Extrinsic){        Flyweight flyweight = null;        if(pool.containsKey(Extrinsic))            flyweight = pool.get(Extrinsic);        else {            flyweight = new ConcreteFlyweight1(Extrinsic);            pool.put(Extrinsic, flyweight);        }        return flyweight;    }}

优缺点：

减少对象的创建，减少内存占用
增加系统复杂度

使用场景

系统中存在大量相似对象
缓冲对象池

注意事项

多线程问题