设计模式之原型模式

概念

原型模式（Prototype），用原型实例指定创建对象的种类，并且通过拷贝这些原型创建新的对象。

优点

• 与每次new对象相比，每NEW一次，都需要执行 一次构造函数，如果构造函数的执行时间很长，那么多次的执行这个初始化操作就实在是太低效了。 一般在初始化的信息不发生变化的情况下，克隆是 最好的办法。这既隐藏了对象创建的细节，又对性能是大大的提高。
• 不用重新初始化对象，而是动态地获得对象运行时的状态

示例

原型接口，包括copy方法用来实现原型对象的克隆

public abstract class Prototype<T> implements Cloneable {
    public T copy() {
        return (T) super.clone();
    }
}

Beast类、OrcBeast类

public abstract class Beast extends Prototype<Beast> {
  public Beast(Beast source) {}
}

public class OrcBeast extends Beast {

  private final String weapon;

  public OrcBeast(OrcBeast orcBeast) {
    super(orcBeast);
    this.weapon = orcBeast.weapon;
  }

  @Override
  public String toString() {
    return "Orcish wolf attacks with " + weapon;
  }
}

不同原型的工厂

public interface HeroFactory {
  Mage createMage();
  Warlord createWarlord();
  Beast createBeast();
}
@RequiredArgsConstructor
public class HeroFactoryImpl implements HeroFactory {

  private final Mage mage;
  private final Warlord warlord;
  private final Beast beast;

  public Mage createMage() {
    return mage.copy();
  }

  public Warlord createWarlord() {
    return warlord.copy();
  }

  public Beast createBeast() {
    return beast.copy();
  }
}

应用

public static void main(String[] args) {
    var factory = new HeroFactoryImpl(
            new ElfMage("cooking"),
            new ElfWarlord("cleaning"),
            new ElfBeast("protecting")
    );
    var mage = factory.createMage();
    var warlord = factory.createWarlord();
    var beast = factory.createBeast();
    LOGGER.info(mage.toString());
    LOGGER.info(warlord.toString());
    LOGGER.info(beast.toString());

    factory = new HeroFactoryImpl(
            new OrcMage("axe"),
            new OrcWarlord("sword"),
            new OrcBeast("laser")
    );
    mage = factory.createMage();
    warlord = factory.createWarlord();
    beast = factory.createBeast();
    LOGGER.info(mage.toString());
    LOGGER.info(warlord.toString());
    LOGGER.info(beast.toString());
}

输出

08:36:19.012 [main] INFO com.iluwatar.prototype.App -- Elven mage helps in cooking
08:36:19.013 [main] INFO com.iluwatar.prototype.App -- Elven warlord helps in cleaning
08:36:19.014 [main] INFO com.iluwatar.prototype.App -- Elven eagle helps in protecting
08:36:19.014 [main] INFO com.iluwatar.prototype.App -- Orcish mage attacks with axe
08:36:19.014 [main] INFO com.iluwatar.prototype.App -- Orcish warlord attacks with sword
08:36:19.014 [main] INFO com.iluwatar.prototype.App -- Orcish wolf attacks with laser

注意

• 需要深拷贝，原型对象的属性又非常复杂的场景，原型模式实现克隆可能会比较复杂
• 可能出现循环引用的问题