Java generics and the Number class

Question

I want to create a method that compares a number but can have an input that is any of the subclasses of Number.

I have looked at doing this in the following manner...

public static <T extends Number> void evaluate(T inputNumber) {
  if (inputNumber >= x) {
    ...
  }
}

I need to get the actual primative before I can perform the comparison, the Number class has methods to retrieve this for each primative but I want a clean way of selecting the correct one.

Is this possible?

Cheers

Answer 1

The Number API doesn't offer a clean way to get the value; you have have to use instanceof.

One solution is to "fold" the values into two types: long and double. That way, you can use this code:

if( inputNumber instanceof Float || inputNumber instanceof Double ) {
    double val = inputNumber.doubleValue();
    ...
} else {
    long val = inputNumber.longValue();
    ...
}

Note that this only works for the standard number types but Number is also implemented by a lot of other types (AtomicInteger, BigDecimal).

If you want to support all types, a trick is to use BigDecimal:

BigDecimal value = new BigDecimal( inputNumber.toString() );

That should always work and give you the most exact result.