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javasuperclassoverriding

Override method with unwanted superclass argument

I have a interface Vector from a library that I use in my project and I cannot modify...

interface Vector<T> {
   public Vector<T> plus(Vector<T> v);
}

Then I implemented it with a class FourVector but the problem arise in overriding method plus. I want FourVector may add only with FourVector, not with all types of Vector! What I try to do is a thing like this (but is obviously wrong)

class FourVector<T> implements Vector<T> {
   public Vector<T>  plus(FourVector<T> v) {
   ...
   }
}

There is some pattern or a workaround that permits the realization of this idea?

Solution

  • If you have a Vector<T>, you will be able at compile time to pass any types of Vector<T> to its add method. That is how the interface is designed.

    So your FourVector is not a real Vector in that respect:

    • either you accept that and don't implement Vector
    • or you can add a runtime check: if (!(v instanceof FourVector)) throw new UnsupportedOperationException("Only FourVector allowed here");