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

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 ...

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, ...

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.