Checkstyle is a development tool to help programmers write Java code that adheres to a coding standard. By default it supports the Google Java Style Guide and Sun Code Conventions, but is highly configurable. It can be invoked with an ANT task and a command line program.
I’m a little out of date with Java, but I believe Checkstyle is currently popular: https://github.com/checkstyle/checkstyle
An extensible media player for Android (by ValveSoftware)
I would strongly suggest your partner start reading other people's code on things like Github, etc., and see how they're written. For example, looking at Valve software's ExoPlayer (here), we can see a number of things:
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