Reactive Principles

reactive ( streams ) graphical explanation
- https://github.com/ReactiveX/RxJava/wiki
- https://reactivex.io/RxJava/2.x/javadoc/2.0.8/io/reactivex/Single.html

Concurrency vs Parallelism

concurent system - multiply actions in progress ( can be/not executed in the same time )
parallel system - multiply actions in progress and executed in the same time ( executed simultaneously )