In this Java 101 tutorial, I’ve explained how interfaces differ from classes, and showed you how to declare, implement, and extend interfaces in your Java programs.

Java 8 has a new package, java.util.function, that contains a number of commonly used functional interfaces. Many are expressed using generics, but there are specializations for primitive types.

The move into functional programming in Java can be intimidating. There were a lot of new interfaces introduced in Java 8 to make working with Streams and lambda expressions possible. But, most of ...