5. Learn the JVM’s Internals
If you are serious about becoming a rockstar Java developer, then you must spend time learning JVM internals, e.g. what are the different parts of the JVM, how they work, JIT, JVM options, Garbage collection, and collectors, etc.
If you know the JVM well, you can write robust and high-performance Java applications, and that’s what rockstar Java developers do.
As part of this, you should also learn how to profile your Java application and how to find performance bottlenecks.
For a structured learning, I recommend The Definitive Guide to Java Performance by Scott Oaks, which is a great book I have read in the last few years.
For those who prefer online courses over books, Understanding the Java Virtual Machine on Pluralsight is also a great collection to master JVM internals.