- SpotBugs (earlier Findbugs) for finding existing bugs. VERY GOOD!
- PMD for finding patterns that can lead to bugs (e.g. unused variables)
- Checkstyle to enforce coding standards and conventions (e.g. whitespace, Javadoc)
- Error Prone hooks right into your application’s compile step
- clang-format supports java and may be available on your system already
All these tools have some overlapping rules. There are many other similar tools, but these are the most popular and supported.