In literature:
For beginners the best option is
Java 8. A beginner's guide - G. Child, for further development and a study of Java:
Java 8. A complete guide - G. Child and
programming Language Java SE 8. Detailed description.
But knowledge of Java is little effective use of it in development, so it will take another literature on Android if you choose like the direction mobile development or the literature on Java EE/Spring, if you choose web or enterprise. In the second case of Russian I can recommend
Spring 4 for professionals,
Spring in action,
Study Java EE 7 and
Java EE 7. The basics. Better to look for the English originals.
Still I recommend to look at the official documentation of Spring Framework and its ecosystem (Boot, Data, Security), as well as dokumentaciju for Java EE. All English, but it's worth it, especially in Spring.
Of third-party technologies we need at least to understand a little XML.
Well, change of direction - the idea is good and useful, the main thing that you was very interesting.
To learn mobile development and then can't hurt. Android has its own architecture, which will need to get used to. - hank51 commented on July 9th 19 at 09:59