Checkstyle is well-known and popular coding style forcing tool.
Build will failed if srouce code violoates condition that defines on checkstyle.xml .
Many other open-source based on java uses Checkstyle, and Checkstyle will help to maintain code quality of the project.

I add some condition for Objectify, and other condtions can be applied step-by-step.
By merging pull-reqeust, future violation of these condition will be cause build failure:

• All the source code must end with newline character.
• Trailing whitespace must not exsits.
• Does not allow two or more consecutive empty lines.
• Deos not allow an empty line before '}'
• Does not allow an empty line after a short line that ends with '{'"