• JDK 21
• Gradle (embedded in the project)

./gradlew clean build

• annotation
• cache
• collections
• common (some uncategorized stuff)
• core
• dynamic
• game
• iterators
• jvm
• multithreading
• numeric
• parser
• proxy
• recursion
• refactoring
• search
• serialization
• sorting
• stream
• string
• tree

Sure, we have tests; they contain some code which describes implementation in a natural way.

SQL folder contains tasks which require writing SQL queries to solve them. Check appropriate video on YouTube

The docs folder contains some notes about interview preparation and useful links. We can perceive materials in this folder as project backlog or "box with other stuff"

Check java-interview-faq-n-answers repo to get materials for preparation to Java verbal interview