How to reduce code by using a superclass?

Question

I would like to refactor some code that currently consists of a superclass and two subclasses.

These are my classes:

public class Animal {     int a;     int b;     int c; }  public class Dog extends Animal {     int d;     int e; }  public class Cat extends Animal {     int f;      int g; } 

This is my current code:

ArrayList<Animal> listAnimal = new ArrayList<>();  if (condition) {     Dog dog = new Dog();     dog.setA(..);     dog.setB(..);     dog.setC(..);     dog.setD(..);     dog.setE(..);        listAnimal.add(dog);  } else {     Cat cat = new Cat();     cat.setA(..);     cat.setB(..);     cat.setC(..);     cat.setF(..);     cat.setG(..);     listAnimal.add(cat); } 

How can I refactor the code regarding the common attributes?

I would like something like that:

Animal animal = new Animal(); animal.setA(..); animal.setB(..); animal.setC(..);  if (condition) {     Dog anim = (Dog) animal; //I know it doesn't work     anim.setD(..);     anim.setE(..);   } else {     Cat anim = (Cat) animal; //I know it doesn't work     anim.setF(..);     anim.setG(..); }  listAnimal.add(anim); 

Answer 1

Your idea to have a variable of type Animal is good. But you also have to make sure to use the right constructor:

Animal animal; // define a variable for whatever animal we will create  if (condition) {     Dog dog = new Dog(); // create a new Dog using the Dog constructor     dog.setD(..);     dog.setE(..);       animal = dog; // let both variables, animal and dog point to the new dog } else {     Cat cat = new Cat();      cat.setF(..);     cat.setG(..);     animal = cat; }  animal.setA(..); // modify either cat or dog using the animal methods animal.setB(..); animal.setC(..);  listAnimal.add(animal); 

Hint: If an Animal is always either Cat or Dog consider making Animal abstract. Then the compiler will automatically complain whenever you try to do new Animal().