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

A great deal of Java programming -- from conditional statements to iterative loops -- deals with the evaluation of true or false values. When you work with the JDK's Streams API and Lambda functions, ...

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 ...

If a lambda body throws an exception, the functional interface method’s throws clause must declare the same exception type or its supertype. Consider Listing 8.