Extending abstract classes and using same methods with different arguments

Question

First of all, here's my abstract class:

public abstract class GeometricObject2D implements Comparable {
  public abstract boolean contains(GeometricObject2D g);
  public abstract boolean contains(double x, double y);
  public abstract boolean overlaps(GeometricObject2D g);
  public abstract int compareTo(Object temp);
  public abstract double getArea();
  public abstract double getPerimeter();

}

I'm supposed to extend it with two other classes, ComparableCircle2D and ComparableRectangle2D. Both contain all of the methods, except that they use their own arguments in the contains and overlaps methods, e.g:

public class ComparableCircle2D extends GeometricObject2D {
//...
  public boolean contains(ComparableCircle2D circle){
  //method
  }
//...
  public boolean overlaps(ComparableCircle2D circle){
  //method
  }
//...
}

This is the error I get:

Error:(1, 8) java: ComparableCircle2D is not abstract and does not override abstract method overlaps(GeometricObject2D) in GeometricObject2D.

Same goes for the other class. I don't fully understand what's wrong, so an explanation and a solution would be greatly appreciated.

P.S: The arguments have to stay the same.

You should use generics instead of raw types when you implement Comparable, i.e implements Comparable<Geometric2DObject> and compareTo(Geometric2DObject other). — Mick Mnemonic
– Mick Mnemonic, Commented Feb 28, 2016 at 15:04

Gabriele Mariotti · Accepted Answer · 2016-02-28 15:25:46Z

2

You can't do it.

In your class you have to override all methods of the abstract class, then you have to override the method:

 @Override
 public boolean contains(GeometricObject2D g){...}

Hovewer you can use somenthing like this:

public abstract class GeometricObject2D<T extends GeometricObject2D> {
     public abstract boolean contains(T g);
}

And in your subclass:

public class ComparableCircle2D extends GeometricObject2D<ComparableCircle2D> {

    @Override 
    public boolean contains(ComparableCircle2D circle){
      //  return....;
    }
}

answered Feb 28, 2016 at 15:25

Gabriele Mariotti

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Comments

Ramanlfc · Accepted Answer · 2016-02-28 14:42:33Z

1

your class must implement/override all methods of the abstract class and interface otherwise you'll have to mark it as abstract.

public boolean contains(ComparableCircle2D circle){

this is not a valid override as the contains() method in GeometricObject2D takes GeometricObject2D

answered Feb 28, 2016 at 14:42

Ramanlfc

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Comments

Yassin Hajaj · Accepted Answer · 2016-02-28 14:45:16Z

1

You must have the exact same arguments to override a method. Hence you're extending a substract class, all the abstract methods have to be implemented.

Here is a solution for you

public boolean contains(GeometricObject2D circle){
    if (!(circle instanceof ComparableCircle2D)) {
        throw InputMismatchException();
    } else {
    // method
    }
}

Or (depending on the logic of your own code)

public boolean contains(GeometricObject2D circle){
    if (!(circle instanceof ComparableCircle2D)) {
        return false;
    } else {
    // method
    }
}

answered Feb 28, 2016 at 14:45

Yassin Hajaj

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