Master core java

Question

What are the most important concepts to master core Java?
I mean if someone wants to master core java what are concepts one must have to know.

Answer 1

regarding account verification

https://www.sololearn.com/discuss/281202/?ref=app

Answer 2

Learn the 3 loops, arraylists and arrays, and hashmaps

Answer 3

thats pretty much the basic core java

Answer 4

Thanks @Edward... Actually I have 3 yrs of exeprience in java technologies like Spring mvc, Hibernate and struts so I know these are the basic things..

My concerns was to know which concepts are very importnat like collection or multithreading and so forth..