[nunobrito]

Oh, please run away from Spring Boot. It is just the new JBoss. That is OK if you want to get inside enterprise software for a living, but that isn't the best usage for Java.

My opinion: learn to create Android apps in Java. Tutorials are good and you get a new set of skills (if not already). After that, focus on learning POJO which is the fundamental knowledge in Java.

Everyone writes stuff in Java/C++ where I work, but less and less Spring Boot is encouraged because of the bloat do debug and performance troubles.