- Compilation model: bytecode/native/whatever
- Are there multiple implementations which are most used and why?
- Package management and versioning
- Common build tools
- Concurrency/io model (async, os threads, green threads, etc)
- Language-specific/more-common data structures
- Sources of UB to aware of
All the "Java for experienced developers" pages I find start by teaching me HelloWorld, move on to declaring variables, loops.... and never get to anything interesting.