How to compare two JSR-363 Quantity objects?

Question

I'm trying to use JSR-363 Quantity to manage some quantities in my application. I have some code similar to the following that I would like to convert to use the Quantity class.

Double volume1 = 14d;
Double volume2 = 18d;

Assert.isTrue(volume1 < volume2);

Using Quantity, I'm trying to find a way to compare two volumes, but there doesn't seem to be anything in the API that's equivalent to the simple comparison above!

Quantity<Volume> volume1 = Quantities.getQuantity(14d, Units.LITRE);
Quantity<Volume> volume2 = Quantities.getQuantity(18d, Units.LITRE);

Assert.isTrue(volume1 < volume2); <--- operator < doesn't exist

What am I missing?

Answer 1

< only works with primitive number types (and boxed equivalents). You cannot use it with objects.

Use volume1.substract(volume2).getValue().doubleValue() < 0 instead.

Answer 2

It turns out that there's a newer specification for units of measurements and a reference implementation that provides ComparableQuantity class that implements java.lang.Comparable.

The newer standard is JSR-385 and its reference implementation is Indriya.

With this one can do:

ComparableQuantity<Volume> volume1 = Quantities.getQuantity(14d, Units.LITRE);
ComparableQuantity<Volume> volume2 = Quantities.getQuantity(18d, Units.LITRE);

Assert.isTrue(volume1.isGreaterThan(volume2));
Assert.isTrue(volume2.isLessThan(volume1));