maven building fails at several point due to organization of tests however even when you bypass test compilation, you get "symbol not found" error in QueryComponent.java.
The reason is that the ShardFieldSortedHitQueue is a class defined in ShardDoc.
class cannot be found during maven compilation although they're under the same package.
Workaroud: if you promote ShardFieldSortedHitQueue to be public, and put it in a file of its own, maven compilation goes well.
There seems to be several boundary problems within core and solrj packages about the tests.