I have been working in Java for more than 8-9 months now. I want to have deep understanding of Java concepts now. For ex: Collections properties, threading, interfaces detailed concepts etc. I mean I have been using all these things for a while now but want to know about the things of Java in detail. Can you suggest some online source/Java book or something like this which I can follow? Usually, I search on web whatever I want to study and read the top 3-4 links. But, some book or course will help me better. Thanks in advance.