Can I add a function to enums in Java?

Question

Hi,

I have an enum, which looks like

public enum Animal {
  ELEPHANT,
  GIRAFFE,
  TURTLE,
  SNAKE,
  FROG
}

and I want to do something like

Animal frog = Animal.FROG;
Animal snake = Animal.SNAKE;

boolean isFrogAmphibian = frog.isAmphibian(); //true
boolean isSnakeAmphibian = snake.isAmphibian(); //false

boolean isFrogReptile = frog.isReptile(); //false
boolean isSnakeReptile = snake.isReptile(); //true

boolean isFrogMammal = frog.isMammal(); //false
boolean isSnakeMammal = snake.isMammal(); //false

I simplified the example for didactic purposes, but this would be really useful to me for my real life example. Can I do it in Java?

Answer 1

Yes, you can. It would look like this:

public enum Animal {
  ELEPHANT(false),
  GIRAFFE(false),
  TURTLE(false),
  SNAKE(false),
  FROG(true);

  private final boolean isAmphibian;

  Animal(boolean isAmphibian) {
    this.isAmphibian = isAmphibian;
  }

  public boolean isAmphibian() {
    return this.isAmphibian;
  }
}

Then you would call it like:

Animal.ELEPHANT.isAmphibian()

Answer 2

yes Enum is a class in Java.

public enum Animal 
{
  ELEPHANT(true),
  GIRAFFE(true),
  TURTLE(false),
  SNAKE(false),
  FROG(false);

  private final boolean mammal; 
  private Animal(final boolean mammal) { this.mammal = mammal; }
  public boolean isMammal() { return this.mammal; }
}

but in your case for a real system I would make that an Enum as well since there is a fixed set of types of animals.

public enum Type
{
  AMPHIBIAN,
  MAMMAL,
  REPTILE,
  BIRD
}

public enum Animal 
{
  ELEPHANT(Type.MAMMAL),
  GIRAFFE(Type.MAMMAL),
  TURTLE(Type.REPTILE),
  SNAKE(Type.REPTILE),
  FROG(Type.AMPHIBIAN);

  private final Type type; 
  private Animal(final Type type) { this.type = type; }
  public boolean isMammal() { return this.type.equals(Type.MAMMAL); }
  public boolean isAmphibian() { return this.type.equals(Type.AMPHIBIAN); }
  public boolean isReptile() { return this.type.equals(Type.REPTILE); }
  // etc...
}

Also note that it is important to make any instance variable final as well.