Question

I’m trying to compare two subclasses of Number inside a class with generics. In the code below, I’m trying to compare Number objects inside an instance of Datum.

How do I enforce that both parameters passed to the Datum constructor are of the same class, so that I can compare what I know to be comparable types – e.g. Float and Float, or Long and Long?

Float f1 = new Float(1.5);
Float f2 = new Float(2.5);

new Datum<Number>(f1, f2);

class Datum<T extends Number> {
    T x;
    T y;

Datum(T xNum, T yNum) {

    x = xNum;
    y = yNum;
            if (x > y) {} // does not compile

    }
}

Answer 1

You could restrict it to Comparable subclasses of Number:

class Datum<T extends Number & Comparable<? super T>> {
  ...

  if (x.compareTo(y) > 0) { ... }
}