In legacy projects sometimes a Java class (with the same fully qualified name) exists in several projects. If you combine these projects, you will never know, which class is used at runtime. It is like Maven dependency hell.
So I wrote a plugin to find out duplicated classes in the classpath. Get it here https://plugins.jetbrains.com/plugin/9663-find-duplicates-inspection, but do not expect much support from me (because it is only a proof-of-concept).