JSR 275 is the new weights-and-measures API for Java. Providing measurements for items that can be processed, translated and operated sounds like a good idea; you can find out more at the proposal page; there's also a write up on JavaWorld.
Unfortunately, the current draft API misspells the SI units of 'metre' and 'litre'. SI stands for "Système International d'Unités", which is a French institution. Correspondingly, the official spelling of the SI units are 'metre' and 'litre'. Other languages or regional variants may be common, but if you're putting together an official API for units should follow the official spellings from the institution that created them.
There's more information on the SI and the official spellings for reference at the BIPM, which incidentally the holder of the world's only exact Kilogram. Did you know there's only one object in the world that weighs exactly a Kilogram? It's the reference mass from which all other Kilogram replicas are made, but there's subtle variants at the microscopic level which means they aren't always the same. Plus, the Kilogram loses/gains mass over time; there's an on-going plan to redefine the kilo as a fixed number of atoms.
Either way, the correct SI spelling of length and volume are 'metre' and 'litre', and those are the ones that should appear in constants in API. If you think the same, send a mail to email@example.com.