Prevent NPE from scala - http://gabrielsw.blogspot.com/2011/10/yes-virginia-scala-can-save-you-from.html

Map scala function to java - http://blogs.sun.com/sundararajan/entry/scala_for_java_programmers
Examples to show good points of Scala - http://edouard.decastro.name/notes/view/1608

Var and Val - http://fruzenshtein.com/scala-variables-values/

Pattern in scala - http://www.scala-lang.org/old/sites/default/files/FrederikThesis.pdf

Effective Programming In Scala – 
https://blog.knoldus.com/2016/06/28/effective-programming-in-scala/
https://blog.knoldus.com/2016/07/13/effective-programming-in-scala-part-2-monads-as-a-way-for-abstract-computations-in-scala//
https://blog.knoldus.com/2016/07/24/effective-programming-in-scala-part-3-powering-up-your-code-implicitly-in-scala/

Reactive, actor, and DB - https://www.javacodegeeks.com/2016/11/scala-tutorial-developing-modern-applications.html

Cheat sheet: The complete guide to Scala - https://jaxenter.com/cheat-sheet-complete-guide-scala-136558.html

libraries-for-data-science - https://medium.com/activewizards-machine-learning-company/top-15-scala-libraries-for-data-science-in-2018-4b2cb5c5367e

Case class for data ( and case object, tuples ) - https://danielasfregola.com/2018/02/01/using-case-classes-to-structure-your-data

Make stacktrace look better - http://www.stackifier.com/scala.html