享元模式

1.定义

它使用共享物件，用来尽可能减少内存使用量以及分享资讯给尽可能多的相似物件；它适合用于只是因重复而导致使用无法令人接受的大量内存的大量物件。主要用于减少创建对象的数量，以减少内存占用和提高性能。这种类型的设计模式属于结构型模式，它提供了减少对象数量从而改善应用所需的对象结构的方式。（例如各种池技术就是使用的享元模式）

2.具体实现

2.1代码

package 设计模式;

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。"));
        f11.operation(new UnsharedConcreteFlyweight("第1次调用b。"));
        f12.operation(new UnsharedConcreteFlyweight("第2次调用b。"));
    }
}
//非享元外部信息
class UnsharedConcreteFlyweight {
    private String info;
    UnsharedConcreteFlyweight(String info) {
        this.info = info;
    }
    public String getInfo() {
        return info;
    }
    public void setInfo(String info) {
        this.info = info;
    }
}
//抽象享元对象
interface Flyweight {
    public void operation(UnsharedConcreteFlyweight state);
}
//具体享元对象
class ConcreteFlyweight implements Flyweight {
    private String key;
    ConcreteFlyweight(String key) {
        this.key = key;
        System.out.println("具体享元" + key + "被创建！");
    }
    @Override
    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;
    }
}