Java in the Small

Paving the On-Ramp
JEP 330: Launch Single-File Source-Code Programs
JEP 458: Launch Multi-File Source-Code Programs
JEP 477: Implicitly Declared Classes and Instance Main Methods (Third Preview)

Examples

https://github.com/cschanck/single-file-java - One file, one piece of functionality. No dependencies.
https://github.com/sormuras/jigsaw-quick-start - Use Java to build Java projects.