Java
A functional Interface
Containing exactly one abstract method.
info
A functional interface is an interface that contains exactly one abstract method. It may contain zero or more default methods and/or static methods.
interface Predicate<T> {
boolean test(T t);
}Why functional interfaces are cool?
A functional interface comes super handy since having only one abstract method is enough for the java compiler to know that when a Simplified Lambda Expressions is called, the method being used is that one.