Java

Can use JavaFX to build a simple GUI

JavaFX is a technology for building Java-based GUIs. Previously it was a part Java itself, but has become a third-party dependency since then. It is now being maintained by OpenJDK.

Can use Java8 streams

Java 8 introduced a number of new features (e.g. Lambdas, Streams) that are not trivial to learn but also extremely useful to know.

Here is an overview of new Java 8 features .(written by Benjamin Winterberg)

Tutorials:

Java 8 Tutorial -- from tutorialspoint.com. Also provides a way to try out code online
Tutorials from Oracle: [Lambdas][Streams]

A video tutorial by well-known Java coach Venkat Subramaniam