【设计模式】结构型设计模式-享元模式的实现

定义

通过共享对象来尽可能减少内存使用和提高性能

UML类图

Java代码

Flyweight接口

interface Flyweight {
    void operation(String extrinsicState);
}

Flyweight实现类

class ConcreteFlyweight implements Flyweight {
    private final String intrinsicState;

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

    @Override
    public void operation(String extrinsicState) {
        System.out.println("Intrinsic State = " + intrinsicState + ", Extrinsic State = " + extrinsicState);
    }
}

享元工厂类

import java.util.HashMap;
import java.util.Map;

class FlyweightFactory {
    private final Map<String, Flyweight> flyweights = new HashMap<>();

    public Flyweight getFlyweight(String key) {
        Flyweight flyweight = flyweights.get(key);
        if (flyweight == null) {
            flyweight = new ConcreteFlyweight(key);
            flyweights.put(key, flyweight);
        }
        return flyweight;
    }
}

使用类

public class FlyweightPatternDemo {
    public static void main(String[] args) {
        FlyweightFactory factory = new FlyweightFactory();

        Flyweight flyweightA = factory.getFlyweight("A");
        flyweightA.operation("First Call");

        Flyweight flyweightB = factory.getFlyweight("B");
        flyweightB.operation("Second Call");

        Flyweight flyweightA2 = factory.getFlyweight("A");
        flyweightA2.operation("Third Call");

        // Note that flyweightA and flyweightA2 are the same instance
        System.out.println(flyweightA == flyweightA2);  // Output: true
    }
}