Java 8 formalized this concept by requiring a functional interface to be annotated with the java.lang.FunctionalInterface annotation type, as in @FunctionalInterface.

Functional interfaces. Java 8 will have a new feature called functional interfaces. Basically, default methods are added to an interface and do not have to be overridden in the interface ...

Traditional Java 8 Predicate example. While the Java 8 Predicate is a functional interface, there's nothing to stop a developer from using it in a traditional manner.Here's a Java Predicate example ...

The functional Predicate interface gets used extensively by the Java 8 Streams API. Any developer who wants to master functional programming in Java will need to be comfortable with the Predicate ...