What I learnt:
I started with the basic concepts of data structures with the help of DS tutorial app.
Then moved onto other concepts with the help of Data Structures Using C and C++ by Y. Langsam, M. Augenstein, A. Tenenbaum and mycodeschool.
Have completed the concepts of oop and practicing it on hackerrank.
Reference: Head First Java.
I will be completing the things that are left and will start with a mini project.