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’s interface language feature confuses many Java newbies. Many mistakenly assume that interfaces only sidestep Java’s failure to support multiple implementation inheritance.

There are over 40 functional interfaces listed in the java.util.functions package, which can make the prospect of functional programming in Java a somewhat daunting task. However, on close inspection, ...