Sort files by name in Java differs from Windows Explorer

Question

I have a simple Java program which reads a file directory and outputs a file list. I sort the files by name:

String [] files = dirlist.list();
files = sort(files);

My problem is that it sorts by name in a different way than Windows Explorer does.

For instance if I have these files: abc1.doc, abc12.doc, abc2.doc.

Java will sort like this:

abc1.doc
abc12.doc
abc2.doc

When I open the folder in Windows Explorer, my files are sorted like this:

abc1.doc
abc2.doc
abc12.doc

How can I make Java sort my files like in Windows Explorer? Is this a Windows trick?

See http://stackoverflow.com/questions/442429/windows-explorer-sort-method — Dean Povey, Jun 18 '10 at 01:58

score 19 · Accepted Answer · answered Jun 18 '10 at 01:55

Windows Explorer uses its own algorithm. In order to sort your files like Explorer does, you should create a custom Comparator to do the trick:

    public class WindowsExplorerStringComparator implements Comparator<String>
    {
      private String str1, str2;
      private int pos1, pos2, len1, len2;

      public int compare(String s1, String s2)
      {
        str1 = s1;
        str2 = s2;
        len1 = str1.length();
        len2 = str2.length();
        pos1 = pos2 = 0;

        int result = 0;
        while (result == 0 && pos1 < len1 && pos2 < len2)
        {
          char ch1 = str1.charAt(pos1);
          char ch2 = str2.charAt(pos2);

          if (Character.isDigit(ch1))
          {
            result = Character.isDigit(ch2) ? compareNumbers() : -1;
          }
          else if (Character.isLetter(ch1))
          {
            result = Character.isLetter(ch2) ? compareOther(true) : 1;
          }
          else
          {
            result = Character.isDigit(ch2) ? 1
                   : Character.isLetter(ch2) ? -1
                   : compareOther(false);
          }

          pos1++;
          pos2++;
        }

        return result == 0 ? len1 - len2 : result;
      }

      private int compareNumbers()
      {
        int end1 = pos1 + 1;
        while (end1 < len1 && Character.isDigit(str1.charAt(end1)))
        {
          end1++;
        }
        int fullLen1 = end1 - pos1;
        while (pos1 < end1 && str1.charAt(pos1) == '0')
        {
          pos1++;
        }

        int end2 = pos2 + 1;
        while (end2 < len2 && Character.isDigit(str2.charAt(end2)))
        {
          end2++;
        }
        int fullLen2 = end2 - pos2;
        while (pos2 < end2 && str2.charAt(pos2) == '0')
        {
          pos2++;
        }

        int delta = (end1 - pos1) - (end2 - pos2);
        if (delta != 0)
        {
          return delta;
        }

        while (pos1 < end1 && pos2 < end2)
        {
          delta = str1.charAt(pos1++) - str2.charAt(pos2++);
          if (delta != 0)
          {
            return delta;
          }
        }

        pos1--;
        pos2--; 

        return fullLen2 - fullLen1;
      }

      private int compareOther(boolean isLetters)
      {
        char ch1 = str1.charAt(pos1);
        char ch2 = str2.charAt(pos2);

        if (ch1 == ch2)
        {
          return 0;
        }

        if (isLetters)
        {
          ch1 = Character.toUpperCase(ch1);
          ch2 = Character.toUpperCase(ch2);
          if (ch1 != ch2)
          {
            ch1 = Character.toLowerCase(ch1);
            ch2 = Character.toLowerCase(ch2);
          }
        }

        return ch1 - ch2;
      }
    }

Now, use it like this:

  Arrays.sort(files, new WindowsExplorerStringComparator());

i wanted to add that: the argument named "files" must be of type String[] — kiltek, May 05 '13 at 18:04

score 3 · Answer 2 · answered Jun 18 '10 at 01:58

3

It looks that way.

However, you can use Arrays.sort() and supply a custom Comparator so that it sorts like Windows Explorer does.

answered Jun 18 '10 at 01:58

ryanprayogo

11,587
11
51
66

score 0 · Answer 3 · edited May 23 '17 at 12:30

0

This is another try to implement it in Java:

Java - Sort Strings like Windows Explorer

In short it splits the two Strings to compare in Letter - Digit Parts and compares this parts in a specific way to achieve this kind of sorting.

With this its IMHO a bit more readable.

edited May 23 '17 at 12:30

Community

1
1

answered May 15 '14 at 06:29

wumpz

8,257
3
30
25

score 0 · Answer 4 · answered Jun 18 '10 at 01:55

0

Sort by string then by name length.

answered Jun 18 '10 at 01:55

Romain Hippeau

24,113
5
60
79

Sort files by name in Java differs from Windows Explorer

4 Answers4