Java how to sort lowercase before uppercase strings

Question

I want the files to be ordered by their abs path name, but I want the lowercase to be sorted before the uppercase. Example: Let\'s say I got 4 files:

files2.         


        

Answer 1

Collections.sort(); lets you pass a custom comparator for ordering. For case insensitive ordering String class provides a static final comparator called CASE_INSENSITIVE_ORDER.

So in your case all that's needed is:

Collections.sort(caps, String.CASE_INSENSITIVE_ORDER);

Answer 2

You can probably use library or utility classes with this behaviour, or you can build your own comparator.

    new Comparator<File>() {
        public int compare(File file1, File file2) {
            // Case-insensitive check
            int comp = file1.getAbsolutePath().compareToIgnoreCase(file2.getAbsolutePath())
            // If case-insensitive different, no need to check case
            if(comp != 0) {
                return comp;
            }
            // Case-insensitive the same, check with case but inverse sign so upper-case comes after lower-case
            return (-file1.getAbsolutePath().compareTo(file2.getAbsolutePath()));
        }
    }

Answer 3

Check the Collator class.

You'll have to read carefully what those constants mean, but one of them should make it possible for you to put lowercase letters before the upper-case letters.

Answer 4

Try this simple implementation :

public static void main(String[] args) {
            List<String> list = new ArrayList<String>();
            list.add("a");
            list.add("b");
            list.add("A");
            list.add("B");
            System.out.println(list);
            Collections.sort(list, new Comparator<String>() {
                    @Override
                    public int compare(String o1, String o2) {
                            if (o1.toLowerCase().equals(o2.toLowerCase())) {
                                    if (o1.toLowerCase().equals(o1)) {
                                            return -1;
                                    } else {
                                            return  1;
                                    }
                            } else {
                                    return o1.toLowerCase().compareTo(o2.toLowerCase());

                            }
                    }
            });
            System.out.println(list);
    }

Answer 5

As suggested by others, Collator does what you want. Writing one of those collator rules looked a bit scary, but it looks like the standard English Collator does exactly what you want:

public static void main(String... args)
{
    List<String> items = Arrays.asList("b", "A", "a", "B");
    Collections.sort(items, Collator.getInstance(Locale.ENGLISH));
    System.out.println(items);
}

gives:

[a, A, b, B]

Answer 6

You could implement your own Comparator, which in turn uses a Collator. See example.