创建子类的新实例

Question

I have an array list of Enemies and each enemy kind extends enemy. Now I don't wan't every same enemy kind to share all their stats, but I base my enemy selection of another array list. So I think the way to go would be to get the object of the array list containing all the options and then changing them to new Instances of the same class. My question is, how would I do that? Or do you guys have a better approach?

For easy of understanding here's what I mean abstracted

class shop{
   ArrayList<Enemy> allEnemies;
}

class generator{
  ArrayList<Enemies> selectedToGenerate = based on some of allEnemies

  for(Enemy x : selectedToGenerate){ // i know this wouldn't work
    x = newInstanceOf(x.getNonenemyThereforeChildclassClass());
  }
}

hope this explains what I mean. Appreciate your time!

Answer 1

You can add a Builder to your Enemy .

abstract class Enemy {
   private int strength;
   public Builder<Enemy> getBuilder();
   public static class Builder<T extends Enemy> {
       int str;
       public Builder<T> copyValues(T enemy) {
           str = enemey.strength;
           return this;
       }
       public Builder<T> strength(int s) {
           str = s;
           return this;
       }
       protected void fillValues(T toFill) {
           toFill.strength = str;
       }
       protected abstract T createInstance();
       public T build() {
           T result = createInstance();
           fillValues(result);
           return result;
       }
   }
}

This Builder can create instances of your Enemy and fill it with values. For subclasses, you can extend the Builder by allowing it to fill more values.

class EnemyA extends EnemyA {
    private int speed;
    public Builder<EnemyA> getBuilder() {
        return new Builder();
    }

    class EnemyABuilder extends Builder<EnemyA> {
        int speed;
        public EnemyABuilder copyValues(EnemyA enemy) {
            super.copyValues(enemy);
            speed = enemy.speed;
        }
        public EnemyABuilder speed(int s) {
            speed = s;
            return this;
        }
        protected void fillValues(EnemyA toFill) {
            super.fillValues(toFill);
            toFill.speed = speed;
        }
        protected EnemyA createInstance() {
            return new EnemyA();
        }
    }
}

Now, you can create copies of the enemies by using their builders:

for(Enemy x : selectedToGenerate){ // i know this wouldn't work
    Builder<? extends Enemy> builder = x.getBuilder();
    builer.copyValues(x);
    Enemy copy = builder.build();
}

As an additional bonus, you can use the builder to quickly create different versions of the same enemy.

EnemyA.Builder base = new Builder().strength(10);
EnemyA withSpeed1 = base.speed(1).build();
EnemyA withSpeed2 = base.speed(2).build();    
EnemyA withSpeed3 = base.speed(3).build();