Going in this direction is a good choice. Being a Java developer and becoming a professional in it is a profession that will pay well in the coming 10 to 20 years for sure and perhaps even later. At the same time, I personally find this technology fascinating and interesting, and after more than 10 years of Java programming and more than 35 years of programming, I still learn something new in it every day.
In this book, you learned the basics of Java programming. From time to time, I also mentioned issues, suggested directions, and warned you about pitfalls that are not Java-specific. However, we also did the homework of learning the Java language, the infrastructure, the libraries, development tools, and networking in Java. You also learned the most modern approaches that came only with Java 8 and 9, such as functional programming in Java, streams, and reactive programming. If you know all that I have written...
