Question

For my Java class, we are learning about interfaces, polymorphism, inheritance, etc.

The homework assignment I am working on is a memory game where you have pairs of cards all face down and you turn over two at a time looking for a match. If they match, they stay visible, if they don’t, the cards are turned back over and you pick two more cards.

My design so far is as follows:

public interface Hideable
  public abstract void hide();
  public abstract void show();    

public interface Speakable
  public abstract String speak();

public interface AnimalCard extends Hideable, Speakable
  public abstract boolean equals(Object obj);

public class Animal implements AnimalCard
  public void hide() { ... }
  public void show() { ... }
  public boolean equals(Object obj) { ... }

  // What do I do for the speak method since a generic Animal
  // can't speak, but I have to provide a definition since the
  // Animal class is implementing the interfaces.

public class Puppy extends Animal
  // Here is where I need to define the speak method.
  public String speak() { ... }

My question is in the comments above. I feel like I’m implementing this incorrectly with regard to the speak() method.

Answer 1

Just make the Animal class abstract.
Concrete classes will have to implement speak(), or be abstract themselves.

public class abstract Animal implements AnimalCard {
    public void hide() { ... }
    public void show() { ... }
    public boolean equals(Object obj) { ... }

There’s no need or value in declaring an abstract method for speak() in Animal – that method is implied by the class hierarchy.