When you run the inner class example, the output would be nine. Java’s Function and lambda expression example. Of course, the whole idea of the functional interface is to incorporate lambda ...

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 ...

That’s not an obvious point when dealing with mathematic functions, but if you look at the first function listed earlier, the following was sufficient to explain everything that was going on: (x) = x ...