I don't usually look for problems if an acceptable solution already exists
Java has 8 pain points for me:
1. Difficulty targeting consoles / iOS
2. No value types / structs, rendering rather a lot of algorithms to be very slow compared to their C implementations or consume vast amounts of memory
3. I don't want operator overloading
but I would rather like to define methods as being infix/prefix/suffix operators
4. A few tiny syntactic sugars like being able to write byte or short literals without the huge ugly cast
5. Fast foreign function interface implementation. Boy am I sick of JNI.
6. No proper multi-dimensional arrays
7. No way to alias ("import blah.bleh.StupidClassWithReallyLongName as ShortName")
8. I really miss C# extension methods but I have a feeling I'm doing something immoral or naughty so the jury's out on that one
It does more or less everything else perfectly well for every use I've so far put it to.