Evolve a basic class in Java

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Hello,

I have the following situation, I have an Animal object and I want to evolve it into a Puppy:

    public class Animal {
        private boolean alive = true;
        public boolean isAlive() {
            return alive;
        }
        public void setAlive(boolean alive) {
            this.alive = alive;
        }
    }

    public abstract class Mamifero extends Animal {
        public abstract void mamar();
    }

    public class Cachorro extends Mamifero {
        @Override
        public void mamar() {
            System.out.println("Done");
        }
    }

I know this (below) does not work:

Animal meuAnimal = new Animal();
Cachorro cao = (Cachorro) meuAnimal;

But I don’t want to have to instantiate a Puppy and go attribute-to-attribute by filling it with the N data that my Animal has.

Is there any way to make this evolution automatically?

java
  • 1

    I’m not sure I understand what you want. If you are instantiating one Cachorro in a certain way is instantiating a Animal. In any case you will have to put the data into the object. You can create a routine that does this or you can create values default for members if this is possible (you did this in this short code). In some cases a constructor may be required to start these values default. But the question doesn’t make it very clear what you want.

  • I possess an animal object (brute), because the class that instigated it is unable to specialize it. After treating this Animal I define that it should be a Dog, so I want to specialize it?

  • 1

    I think the "less worse" option would be to create an animal builder who receives an animal as a parameter. So when you convert it to other animals, you would do something like: Cachorro cao = new Cachorro(animal); And regardless of what kind of animal you instantiated you would only need to keep sending the animal(parameter) to the Animal class.

  • Animal meuAnimal = new Cachorro(); but you can only use the methods present in the Animal class

  • @Christianberegula you will answer?

  • You are experiencing a typical problem caused by the use of inheritance by yourself and not to solve a real problem: the promotion of an existing object to a more specialized type object. There is no such thing in practice - a dog is born a dog, it is not born an undefined type of animal to turn into a dog later on. The same is true in modeling a real problem in a real domain - if you notice the need to promote an object to a type below in the hierarchy, it’s because you used inheritance when you shouldn’t have.

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2 answers

4


I had actually thought a little differently. I would look something like this:

    public class Animal {
        private boolean alive = true;
        public Animal() {
        }
        public Animal(Animal animal) {
            this.alive = animal.alive;
        }
        public boolean isAlive() {
            return alive;
        }
        public void setAlive(boolean alive) {
            this.alive = alive;
        }
    }

The animal class would have a builder with an animal as a parameter.

    public abstract class Mamifero extends Animal {
        public Mamifero() {
        }
        public Mamifero(Animal animal) {
            super(animal);
        }
        public abstract void mamar();
    }

Like all his descendants...

    public class Cachorro extends Mamifero {
        public Cachorro() {
        }
        public Cachorro(Animal animal) {
            super(animal);
        }
        @Override
        public void mamar() {
            System.out.println("Done");
        }
    }

And during the execution of the code you would only need to instantiate your new type of animal.

Cachorro cao = new Cachorro(animal);
Gato gato = new Gato(animal);
Vaca vaca = new Vaca(animal);

And the only class that would care to redistribute those values would be the Animal class.

  • I also found this in other questions ( http://stackoverflow.com/questions/4033118/how-to-downcast-java-object ), but it does not escape from this solution. In the case of this link the guy suggests a class of Factory.

1

"Is there any way I can instantiate a Puppy based on an existing Animal object?"

Do the following: Create a constructor in the Puppy class that receives an Animal as a parameter and pass the values of that Animal object to that Puppy class.

  • Example

You got that class Animal:

public class Animal {

  int atributo1;
  double atributo2;
  String atributo3;

  public void setAtributo1(int atributo) {
    atributo1 = atributo;
  }

  public int getAtributo1() {
    return this.atributo1;
  }

  public void setAtributo2(double atributo) {
    atributo2 = atributo;
  }

  public void getAtributo2() {
    return this.atributo2;
  }

  public void setAtributo3(String atributo) {
    atributo3 = atributo;
  }

  public void getAtributo3() {
    return this.atributo3;
  }

}

Your Puppy class should be as follows

public class Cachorro {

  public Cachorro(Animal animal) {

    this.setAtributo1(animal.getAtributo1());   
    this.setAtributo2(animal.getAtributo2());
    this.setAtributo3(animal.getAtributo3());

  }

}

Thus, when instantiating the objects you will do as follows:

Animal meuAnimal = new Animal();

meuAnimal.setAtributo1(/*VALOR*/);
meuAnimal.setAtributo2(/*VALOR*/);
meuAnimal.setAtributo3(/*VALOR*/);

Cachorro cao = new Cachorro(meuAnimal);

  • I think what he wants is to do that but use the special methods of Cachorro

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