It's IntelliJ editors plugin which will help you to rename class parameters to match the regular expression ^?[_a-z][a-zA-Z0-9]*?$ and format the file content.
It's useful to respect syntax and have code cleaned. Shared naming conventions allow teams to collaborate effectively.
Simply open any Jetbrains's editors and go to File -> Settings -> Plugins. You search for this plugin in the Marketplace. It does not require after installation, any editor restart.