Functional Programming in Java

Listing Immediate Subdirectories Using flatMap

We saw how to list the members of a given directory. Let’s look at the effort to explore the immediate (one level deep) subdirectories in a given directory, first using a rudimentary operation and then, more conveniently, using the flatMap method.

Let’s use the traditional for loop first to iterate over the files in a given directory. If a subdirectory contains any files, we’ll add them to our list; otherwise, we’ll add the subdirectory itself to the list. Finally, we’ll print the total number of files found. Here’s the code—for the hard way.