Tutorials

http://docs.oracle.com/javase/tutorial/

https://codingbat.com/java

https://codestepbystep.com/problem/list/java

https://practiceit.cs.washington.edu/

http://csteachingtips.org/tips-for-tutors

ebooks

http://www.mkyong.com/featured/top-5-free-java-ebooks/

http://math.hws.edu/javanotes/

http://www.mindviewinc.com/Books/downloads.html