Java: Create particular child class object in Java

Question

So let's suppose that I have a class Animal in Java, and 3 child classes. The structure looks like this

class Animal{
  ...
  public breed(){
    //create a new child class object here
  }
}

class Bird extends Animal{
  ...
}

class Bear extends Animal{
  ...
}
class Frog extends Animal{
  ...
}

I want to create another object in breed class, but I want to create an object of the same child class, from which the method breed() was executed. For instance, if frog.breed() was executed I want to create a new Frog object there (assumming frog is a Frog object), if bear.breed() was executed I want to create a new bear object etc.

Is there any way to handle it in animal class, or I have to override method in every child class?

Michael · Accepted Answer · 2021-06-02 09:57:11Z

It's possible if you pass a reference to a function. I suspect method references and passing functions as arguments may be a bit beyond your level right now, but it's not that complicated.

class Animal {
  private final Supplier<Animal> ctor;

  Animal(Supplier<Animal> ctor) {
      this.ctor = ctor;
  }

  public Animal breed() {
    return ctor.get();
  }
}

class Bird extends Animal {
  public Bird() {
    super(Bird::new);
  }
}

The advantage of overriding is that Java allows to you make the return type more specific. So if you have a Bird bird; you could do Bird chick = bird.breed();.

class Bird extends Animal {
  public Bird breed() { //super return type is Animal, this return type is more specific
    return new Bird();
  }
}

Without overriding, you can't make the return type more specific, so you would have to assign it to a variable of type Animal chick = bird.breed(), unless you were to cast it.

Also achievable with reflection, but you should avoid it if possible.

Serhii Vasniev · Accepted Answer · 2021-06-02 10:02:45Z

0

Yes, you can do it, using reflection. But this approach isn't recommended, cause it's error-prone and you should consider rather using standard Java inheritance constructions. Example with recursion:

class Animal{

    public Animal breed() throws InstantiationException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        return this.getClass().getDeclaredConstructor().newInstance();
    }
}

edited Jun 2, 2021 at 10:02

answered Jun 2, 2021 at 9:57

Serhii Vasniev

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