What's too bad is that Java had a chance to handle alternatives properly as sum types, when enums were being added. But the designers chose instead of sum type

What's too bad is that Java had a chance to handle alternatives properly as sum types, when enums were being added. But the designers chose instead of sum types, to add them as yet another kind of "object" that have to have a common constructor (and thus the exact same backing data) and methods. So basically all the variants have to be of the same "shape". Very disappointing!