Listing 8 defines a first-class function named add() with a parameter x and a nested function partialAdd(). The nested function partialAdd() has access to x because x is in add() ‘s lexical scope.

While this sounds pretty straightforward, it doesn’t quite telegraph the kind of power you have with first-class functions. If you write JavaScript, you have probably used higher-order functions ...

java.util.function.UnaryOperator @FunctionalInterface public interface UnaryOperator<T> extends Function<T,T> T apply(T t) Applies this function to the given argument. Parameter Types: T - the input ...