The API is just cURL requests, a number of examples are in javascript, but they are just examples to show how to do it in that language.
If you are looking for a library to help theres:
- https://github.com/twitch4j/twitch4j
- https://github.com/Gikkman/Java-Twirk
- https://gitlab.com/veteran-software/java/twava
- https://github.com/GlitchLib/glitch
Which are just four that are represented the Twitch API discord server. Or you can join other java devs for more real time help in the java room of the TwitchApp server https://dev.twitch.tv/support/