This plugin is included in the Java Ecosystem.
It uses FindBugs to provide coding rules.
SonarQube Java Plugin
In the quality profile, activate some rules from FindBugs and run an analysis on your project.
FindBugs requires the compiled classes to run.
Make sure that you compile your source code with debug information on (to get the line numbers in the Java bytecode). Debug is usually on by default unless you're compiling with Ant, in which case, you will need to turn it on explicitly. If the debug information is not available, the issues raised by FindBugs will be displayed at the beginning of the file because the correct line numbers were not available.