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

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

实现

public interface Flyweight {
    void doOperation(String extrinsicState);
}
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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);
    }
}
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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);
    }
}
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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");
    }
}
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Object address: 1163157884
IntrinsicState: aa
ExtrinsicState: x
Object address: 1163157884
IntrinsicState: aa
ExtrinsicState: y
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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)

联系我

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