If you are a new Java programmer, go over fundamental Java concepts, data structure, algorithms and API. Experienced programmers may benefit from reviewing core Java concepts like concurrency, OOPs, exception handling, string handling, synchronisation, collection framework and multi-threading. You can also study advanced Java topics like JDBC, JSP and Servlet, and popular frameworks like JSF, Hibernate ORM framework, Spring with Core, MVC, AOP, JDBC and ORM, Struts and SOAP & REST web services.