How I can skip one method in a class extending Abstract Class?

Question

I have one abstract class named Animal having around 100 methods including swim .

Many classes such as Dog,Cat ,Lion are extending that class.

Now there is one animal Giraffe which can't swim. But it is extending Animal abstract class.

I want that giraffe object does not have swim method.

Giraffe g = new Giraffe();
//g.swim();  // This swim should not come.

I cant change the Animal Class. One solution is to create One more abstract class copying all the methods except swim. But this is not a good approach.

How I can do this using Animal abstract class? Thank in advance.

Answer 1

You can't cause java guides by contract. If you are saying that an Animal can swim then all animals can swim including a Giraffe, if it's not , then the giraffe it's not an animal.

The only thing you can do are without changing Animal

@Override
public void swim(){
 throw new UnsupportedOperationException();
}

The other thing you can do is making another class

public class Giraffe {

private final Animal a;

public Giraffe(Animal a){
  this.a=a;
}

public void method1(){
  a.method1();
}

public Something drink(){
  return a.drink();
}
.
.
.
// and not implementing swim 
}

Another is making a super-interface for Animal that don't have swim() method and make Animal implement it.

Answer 2

You cannot skip the definition of swim() . However, you can throw an exception for such cases.

void swim() throws CanNotSwimException{
}

Answer 3

我认为，最优雅的解决方案是重写方法，并抛出OperationNotSupportedException

Answer 4

根据情况，如果方法为void ，则也可以将其保留为空白。