The app consists of all the necessary and important theoretical points on below mentioned topics of java programming language:
(For in-depth and learning from scratch, please refer the paid version)

1. Compile and Execute
2. Class Members
3. Method Overloading
4. Execution Process in JVM
5. Constructors
6. Initialization Blocks
7. OOPS - Encapsulation
8. Inheritance
9. Polymorphism
10. Abstraction
11. Final and Interfaces
12. Exceptions - Introduction
13. More on Exceptions
14. Wrapper Classes
15. Multi-Threading
16. Synchronization
17. Inner Classes and Patterns
18. Collections
19. File Handling
20. Serialization
21. JDBC-1
22. JDBC-2
23. XML
24. Web Applications
25. Servlet Life Cycle
26. Request Dispatching
27. Session Management
28. Java Server Pages
29. JSP Implicit Objects
30. JSP Directives

However, the app is not for beginners. This could be helpful for brush up purpose for those who are already having good exposure on this programming language.