Java sort String array of file names by their extension

Question

I have an array of filenames and need to sort that array by the extensions of the filename. Is there an easy way to do this?

Answer 1

If you just want to group the files by their extension and do not care about the actual alphabetical order, you can use this:

I think the simplest thing you can do that also works when the filenname does not have a "." is to just reverse the names and compare them.

Arrays.sort(ary, new Comparator<String>() {
    @Override
    public int compare(String o1, String o2) {
        String r1 = new StringBuffer(o1).reverse().toString();
        String r2 = new StringBuffer(o2).reverse().toString();
        return r1.compareTo(r2);
    }
});

Its a shame that java's string does not even have a reverse().

Answer 2

Create your own Comparator that treats the strings as filenames and compares them based on the extensions. Then use Arrays.sort with the Comparator argument.