Sorting String List by rules

Question

How to sort string list apart from ascending or descending order based on ACII table using comparator or comparable.

Let us assume that a string list contains words which starts with either number (1start) or special character (@fill) or lowercase (kind) or uppercase (Link)

Sample scenario: I would like to sort the list in this particular order: (sorting an be either asc or desc)

• words which starts with 'lowercase' should be sorted first,
• words which starts with 'special' character should be sorted second,
• words which starts with 'number' should be sorted third,
• words which starts with 'uppercase' should be sorted fourth

Answer 1

I'd create an enum for each of these "character classes", with some logic to figure out what class each character belongs to:

public enum CharacterClass {
    LOWERCASE, SPECIAL, NUMBER, UPPERCASE;

    public static CharacterClass getClass(char c) {
        if (Character.isLowerCase(c)) {
            return LOWERCASE;
        }
        if (Character.isUpperCase(c)) {
            return UPPERCASE;
        }
        if (Character.isDigit(c)) {
            return NUMBER;
        }
        return SPECIAL;
    }
}

Based on that, we can now create a comparator that goes over the characters of two strings and compares their classes (and then the characters themselves, if they have the same class):

public class CharacterClassComparator implements Comparator<String> {
    @Override
    public int compare(String o1, String o2) {
        int l1 = o1.length();
        int l2 = o2.length();
        int length = Math.min(l1, l2);

        for (int i = 0; i < length; ++i) {
            char c1 = o1.charAt(i);
            char c2 = o2.charAt(i);

            // Compare the character classes
            int res = CharacterClass.getClass(c1).compareTo(CharacterClass.getClass(c2));
            if (res != 0) {
                return res;
            }

            // If the clases are the same, compare the actual characters
            res = Character.compare(c1, c2);
            if (res != 0) {
                return res;
            }
        }

        // All the characters up to the shared length are the same
        // Compare the lengths:
        return Integer.compare(l1, l2);
    }
}