设计模式 – 享元模式（Flyweight Pattern）

享元模式（Flyweight Pattern）是一种结构型设计模式，它通过共享已经存在的对象，减少系统中对象的数量，以降低内存占用和计算开销。享元模式主要用于处理大量相似对象的情况，它可以有效地减小内存消耗，提高性能。

以下是一个简单的Java实现：

1. 创建享元接口（Flyweight Interface），表示享元对象的接口：

public interface Flyweight {
    void operation(String externalState);
}

2. 创建具体享元类（Concrete Flyweight），实现享元接口：

public class ConcreteFlyweight implements Flyweight {
    private String internalState;

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

    @Override
    public void operation(String externalState) {
        System.out.println("Internal State: " + internalState + ", External State: " + externalState);
    }
}

3. 创建享元工厂类（Flyweight Factory），用于创建和管理享元对象：

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

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

    public FlyweightFactory() {
        flyweights = new HashMap<>();
    }

    public Flyweight getFlyweight(String key) {
        if (!flyweights.containsKey(key)) {
            flyweights.put(key, new ConcreteFlyweight(key));
        }
        return flyweights.get(key);
    }
}

4. 使用享元模式创建对象：

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

        Flyweight flyweight1 = flyweightFactory.getFlyweight("A");
        flyweight1.operation("Red");

        Flyweight flyweight2 = flyweightFactory.getFlyweight("B");
        flyweight2.operation("Blue");

        Flyweight flyweight3 = flyweightFactory.getFlyweight("A");
        flyweight3.operation("Green");

        System.out.println("flyweight1 == flyweight3: " + (flyweight1 == flyweight3));
    }
}

运行上述代码，你将看到：

Internal State: A, External State: Red
Internal State: B, External State: Blue
Internal State: A, External State: Green
flyweight1 == flyweight3: true

享元模式通过共享已经存在的对象，减少系统中对象的数量，以降低内存占用和计算开销。这种模式在处理大量相似对象的情况时非常有用，它可以有效地减小内存消耗，提高性能。