Introduction to Programming

What is a functional interface?

In fact, you have already seen elements of functional programming in our demonstration code. One example is the forEach(Consumer consumer) method, available for every Iterable, where Consumer is a functional interface. Another example is the removeIf(Predicate predicate) method, available for every Collection object. The passed-in Predicate object is a function – an implementation of a functional interface. Similarly, the sort(Comparator comparator) and replaceAll(UnaryOperator uo) methods in the List interface and several compute() methods in Map are examples of functional programming.

A functional interface is an interface that has only one abstract method, including those that were inherited from the parent ...