Hi, While working on a [small contribution](https://issues.apache.org/jira/browse/MATH-1426) I noticed that there's a checkstyle setup which is run in a reporting phase of Maven which might be skipped by most developers and isn't used on Travis CI. I suggest to move this phase to the validate phase of Maven which runs before the compile and test phase and in case of failure forbids the invoker to build the project successfully. Therefore most contributions will like they're intended too without the need of extra communication.
The downside is that new (and eventually old) devs might be annoyed at some point, especially if they frequently work on different projects with different styles. I can take over the move to the validate phase which is 10 lines insertion/deletion in pom.xml, but not the definition of code style rules which are common for the project because I don't know them. Doing this change reveals about 400 issues of which > 95% are related to missing or errornous Javadoc which is worth having a look at, but might be postponed by deactivating the rule for now. Then you need to discuss code style rules, because some, like the ones in the issue linked above, aren't covered yet. -Kalle Richter
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