设计模式学习—22享元模式

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享元模式

UML

解释说明

• 享元模式：运用共享技术有效地支持大量细粒度的对象。
• 享元模式可以避免大量非常相似的类的开销，以降低内存的消耗。在程序设计中，有时需要生成大量细粒度的类实例来表示数据。如果这些实例除了几个参数外基本相同，就能够大幅度减少需要实例化的类的数量。把哪些参数参数转移到享元类外，再在需要的时候传递进来。
• 注意：享元模式的使用会给程序带来逻辑的复杂性。

代码实现

• Flyweight.class

package learn22;

public abstract class Flyweight {
    public abstract void operation(int extrinsicState);
}

• UnsharedConcreteFlyweight.class

package learn22;

public class UnsharedConcreteFlyweight extends Flyweight {
    @Override
    public void operation(int extrinsicState) {
        System.out.println("执行不共享的UnsharedConcreteFlyweight" + extrinsicState);
    }
}

• ConcreteFlyweight.class

package learn22;

public class ConcreteFlyweight extends Flyweight {
    @Override
    public void operation(int extrinsicState) {
        System.out.println("执行ConcreteFlyweight" + extrinsicState);
    }
}

• FlyweightFactory.class

package learn22;

import java.util.Hashtable;

public class FlyweightFactory {
    private Hashtable flyweights = new Hashtable();

    public FlyweightFactory() {
        flyweights.put("X", new ConcreteFlyweight());
        flyweights.put("Y", new ConcreteFlyweight());
        flyweights.put("Z", new ConcreteFlyweight());
    }

    public Flyweight getFlyweight(String key) {
        return (Flyweight) flyweights.get(key);
    }
}

• UnsharedConcreteFlyweight.class

package learn22;

public class UnsharedConcreteFlyweight extends Flyweight {
    @Override
    public void operation(int extrinsicState) {
        System.out.println("执行不共享的UnsharedConcreteFlyweight" + extrinsicState);
    }
}

参考资料

• 大话设计模式