结构型 - 享元(Flyweight)

享元模式(Flyweight Pattern): 利用共享的方式来支持大量细粒度的对象，这些对象一部分内部状态是相同的。 它让某个类的一个实例能用来提供许多"虚拟实例"。@pdai

• 结构型 - 享元(Flyweight)

• 意图

• 类图

• 实现

• JDK

意图

利用共享的方式来支持大量细粒度的对象，这些对象一部分内部状态是相同的。

类图

• Flyweight: 享元对象
• IntrinsicState: 内部状态，享元对象共享内部状态
• ExtrinsicState: 外部状态，每个享元对象的外部状态不同

d52270b4-9097-4667-9f18-f405fc661c99.png

实现

    public interface Flyweight {
        void doOperation(String extrinsicState);
    }

    public class ConcreteFlyweight implements Flyweight {

        private String intrinsicState;

        public ConcreteFlyweight(String intrinsicState) {
            this.intrinsicState = intrinsicState;
        }

        @Override
        public void doOperation(String extrinsicState) {
            System.out.println("Object address: " + System.identityHashCode(this));
            System.out.println("IntrinsicState: " + intrinsicState);
            System.out.println("ExtrinsicState: " + extrinsicState);
        }
    }

    public class FlyweightFactory {

        private HashMap<String, Flyweight> flyweights = new HashMap<>();

        Flyweight getFlyweight(String intrinsicState) {
            if (!flyweights.containsKey(intrinsicState)) {
                Flyweight flyweight = new ConcreteFlyweight(intrinsicState);
                flyweights.put(intrinsicState, flyweight);
            }
            return flyweights.get(intrinsicState);
        }
    }

    public class Client {
        public static void main(String[] args) {
            FlyweightFactory factory = new FlyweightFactory();
            Flyweight flyweight1 = factory.getFlyweight("aa");
            Flyweight flyweight2 = factory.getFlyweight("aa");
            flyweight1.doOperation("x");
            flyweight2.doOperation("y");
        }
    }

    Object address: 1163157884
    IntrinsicState: aa
    ExtrinsicState: x
    Object address: 1163157884
    IntrinsicState: aa
    ExtrinsicState: y

JDK

Java 利用缓存来加速大量小对象的访问时间。

• java.lang.Integer#valueOf(int)
• java.lang.Boolean#valueOf(boolean)
• java.lang.Byte#valueOf(byte)
• java.lang.Character#valueOf(char)