I'm guessing the reason for making this program was just a bit of experimenting or playing around? I doubt the intention was to make something to be able to type hiragana in general for websites and documents (at least I hope not...)
Being able to code this in java could be useful if you're planning to make something like Japanese language learning software. Like if you were to make a game to learn to recognise kana, then you could make use of this thing you've made so far. I used to think about making stuff like this. ^^
For a proper Japanese input method software though, I'd suggest getting Google Japanese Input. Here's the official direct download page for it:
https://tools.google.com/dlpage/japaneseinput/eula.htmlFebruary 7, 2015 at 1:20pm