设计模式11 享元模式

享元模式定义：运用共享技术来有効地支持大量细粒度对象的复用。它通过共享已经存在的对象来大幅度减少需要创建的对象数量、避免大量相似类的开销，从而提高系统资源的利用率。享元可以理解为“共享元件”。

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。

共享元件：

public interface Flyweight {
    public void operation(UnsharableFlyweight unsharableFlyweight);
}

public class ConcreteFlyweightA implements Flyweight {
    private String key;

    public ConcreteFlyweightA(String key) {
        this.key = key;
    }

    @Override
    public void operation(UnsharableFlyweight unsharableFlyweight) {
        System.out.print("具体享元" + key + "被调用，");
        System.out.println("非享元信息是:" + unsharableFlyweight.getInfo());
    }
}

public class ConcreteFlyweightB implements Flyweight {
    private String key;

    public ConcreteFlyweightB(String key) {
        this.key = key;
    }
    @Override
    public void operation(UnsharableFlyweight unsharableFlyweight) {
        // TODO Auto-generated method stub
        System.out.print("具体享元" + key + "被调用，");
        System.out.println("非享元信息是:" + unsharableFlyweight.getInfo());
    }
}

非共享元件：

public class UnsharableFlyweight {
    private String info;

    public UnsharableFlyweight(String info) {
        this.info = info;
    }

    public String getInfo() {
        return info;
    }

    public void setInfo(String info) {
        this.info = info;
    }
}

元件工厂：

public class FlyweightFactory {
    private HashMap<String, Flyweight> flyweights;

    public FlyweightFactory() {
        flyweights = new HashMap<String, Flyweight>();
        flyweights.put("A", null);
        flyweights.put("B", null);
    }

    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，直接返回");
        } else {
            if (key == "A") {
                System.out.println("具体享元" + key + "不存在，新生成A");
                flyweight = new ConcreteFlyweightA(key);
                flyweights.put(key, flyweight);
            } else {
                System.out.println("具体享元" + key + "不存在，新生成B");
                flyweight = new ConcreteFlyweightB(key);
                flyweights.put(key, flyweight);
            }
        }
        return flyweight;
    }
}

调用方式：

public class Client {
    //线程池，数据库连接池
    public static void main(String[] args) {
        FlyweightFactory factory = new FlyweightFactory();
        Flyweight f1 = factory.getFlyweight("A");
        f1.operation(new UnsharableFlyweight("第1次调用A"));
        System.out.println("----------------------");
        
        Flyweight f2 = factory.getFlyweight("A");
        f2.operation(new UnsharableFlyweight("第2次调用A"));
        System.out.println("----------------------");
        
        Flyweight f3 = factory.getFlyweight("A");
        f3.operation(new UnsharableFlyweight("第3次调用B"));
        System.out.println("----------------------");
        
        Flyweight f4 = factory.getFlyweight("B");
        f4.operation(new UnsharableFlyweight("第1次调用B"));
        System.out.println("----------------------");
        
        Flyweight f5 = factory.getFlyweight("B");
        f5.operation(new UnsharableFlyweight("第2次调用B"));
        System.out.println("----------------------");
    }
}

执行结果：

 享元模式一般使用哈希数据结构实现。