You can find all the details here:

IDEA-170117"objc: Class JavaLaunchHelper is implemented in both ..." warning in Run consoles

It's the old bug in on Mac that got triggered by the  Agent being used by the IDE when starting the app. This message is harmless and is safe to ignore.  developer's comment:

The message is benign, there is no negative impact fromthis problem since both copies of that class are identical (compiled from the exact same source). It is purely a cosmetic issue.

The problem is fixed in Java 9 and in Java8 update 152.

If it annoys you or affects your apps in any way, the workaroundfor IntelliJ IDEA is to disable idea_rt launcher agent by addingidea.no.launcher=true into idea.properties (Help | Edit Custom Properties...).