For me being confident in following, is absolutely must to succeed in interviews or as a java developer-
1)Generics
2)Collections
3)nifty features of java 8
4)Oops
5)Design
patterns.
6)Every interview I attended before landing a job, I was asked in different permutations about Comparable and comparator. Weird.
7) Learn spring. It is easy and every other company uses it.
8) exception handling and caveats.
Also interviews tend to focus on the weird and whacky. Spend some time on edge cases.
9)final, finally and finalise. Another weird one. But beginners often fumble.
10) A touch up on multithreading.
That's all I can think of. Good luck