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.

We can implement macros in Java SE6 with JSR-223. ... One cool feature in JSR-223 is to allow scripts to implement Java interfaces. For example, we wish to implement the ActionListener interface.

So to learn Java lambda syntax, you need to be familiar with its three component parts: The argument list; The arrow; The method body; To apply these concepts, we first need a functional interface. A ...

java.util.function.UnaryOperator @FunctionalInterface public interface UnaryOperator<T> extends Function<T,T> T apply(T t) Applies this function to the given argument. Parameter Types: T - the input ...

For an introduction to Java interfaces, including the difference between classes and interfaces, see my Java 101 tutorial Working with interfaces in Java. Nesting interfaces in classes.