Conversion between numeric objects in Java

Question

I am looking for a simple, concise way to convert a given Number object to an object of a given numeric type.

• Loss of precision due to narrowing conversions is fine
• I prefer not to go through strings.

I need something like:

private static Number convert(Number num, Class<? extends Number> targetType)

Is there a way to do it without checking all the combinations of types?

Answer 1

Perhaps converting via BigDecimal would work?

Answer 2

You can use something like:

String simpleName = targetType.getSimpleName().toLowerCase();
if (simpleName.equals("integer")) {
   simpleName = "int";
}
Method m = number.getClass().getMethod(simpleName + "Value");
return (Number) m.invoke(number);

This relies on the fact that Number has methods like longValue(), floatValue(), etc.

As for BigInteger or AtomicInteger - you can use their constructor reflectively, which accepts one argument - the primitive type.

Answer 3

I think the clearest way is to use brute force:

private static Number convert(Number num, Class<? extends Number> targetType) {
    Number result = null;
    if (Byte.class.equals(targetType)) {
        result = Byte.valueOf(num.byteValue());
    } else if (Short.class.equals(targetType)) {
        result = Short.valueOf(num.shortValue());
    } else if (...) {
         ...
    } else {
        throw new IllegalArgumentException("targetType is not a Number");
    }
    return result;
}

You might use reflection, but I find that more hackish.