Java References
There is a lot of concepts and libraries available to know and learn about Java. Few are mentioned below, I will try to update the list with maximum coverage.
Starters
The 2021 Java Programmer RoadMap
Execution Engine in JVM | JVM Architecture | JAVA
First step toward learning
10 Basic Programming Principles Every Programmer Must Know
SOLID Design Principles Explained: The Single Responsibility Principle
What is Functional Programming? Tutorial with Example
Video courses
Top 5 Online Courses to learn Functional Programming in Java - Best of Lot
Advanced concepts
Top 10 Object-Oriented Design Principles for writing Clean Code
The 2021 Frontend and Backend Developer RoadMap
Code Review Checklist – To Perform Effective Code Reviews