Java list sort by name(integers)

Question

I have a list of file names that are named like 0.jpg,1.jpg etc.. and I want to order them in descending fashion but seems that I'm having trouble doing that. Also I've noticed that the ascending ordering is not quite like I want to, here is an example:

file 1.jpg
file 10.jpg
file 100.jpg
file 101.jpg
...
file 109.jpg
file 11.jpg

So my question is how can I do a descending ordering but correctly? Here is what im I doing right now:

Collections.sort(files, new Comparator<File>() {
                @Override
                public int compare(File s1, File s2) {
                    return s1.getName().compareToIgnoreCase(s2.getName());
                }
            });

http://stackoverflow.com/questions/104599/sort-on-a-string-that-may-contain-a-number and http://www.davekoelle.com/alphanum.html — user370305, Mar 18 '15 at 15:40
@user370305 your coment led me to the answer, please submit your answer so I can accept it — Darko Petkovski, Mar 18 '15 at 15:54

score 2 · Answer 1 · answered Mar 18 '15 at 15:42

Try (only works if the files had the same name pattern ie: 'file xxx.jpg')

Collections.sort(files, new Comparator<File>() {
                @Override
                public int compare(File s1, File s2) {
                    int f1 = Integer.parseInt(s1.getName().replace("file ", "").replace(".jpg",""));
                    int f2 = Integer.parseInt(s2.getName().replace("file ", "").replace(".jpg",""));
                    return f1 > f2?-1:(f1==f2?0:1);
                }
            });

I guess this should work, but the answer was in the comment from @user370305 Thanks! — Darko Petkovski, Mar 18 '15 at 15:53

score 0 · Answer 2 · answered Mar 18 '15 at 15:45

File.getName() returns a String, obviously, so this ordering (1, then 10, then 100) is expected. You need to extract the numerical part from the string (e.g. using a regular expression), parse the integer if it's there (e.g. if the captured substring length is greater than zero) and compare the integers.

score 0 · Answer 3 · answered Mar 18 '15 at 15:48

You should parse the name of the files before calling the method Try this :

Arrays.sort(fileArray, new Comparator<File>() {
public int compare(File file1, File file2) {
    try {
        int i = Integer.parseInt(file1.getName());
        int j = Integer.parseInt(file2.getName());
        return i - j;
    } catch(NumberFormatException e) {
        throw new AssertionError(e);
    }
} });

Java list sort by name(integers)

3 Answers3