Custom treemap sorting

Question

I need to use map collection and I decided to use treemap (because of sorted keys). However, treemap sorts alphabetically my list from "A -> Z" and then "a -> z". For example input = zgaZGA output = AGZagz

Do anyone have any idea how to sort it beginning from lower case? (I mean to have output = agzAGZ)

I'm writing in Java language (Java SE8) Thanks for any help!

Answer 1

You can provide your own custom Comparator:

public class LowerCaseFirstComaparor implements Comparator<Character> {
    @Override
    public int compare (Character c1, Character c2) {
        if (Character.isLowerCase(c1)) {
            if (Character.isLowerCase(c2)) {
                return c1.compareTo(c2);
            } else {
                return -1;
            }
        } else if (Character.isLowerCase(c2)) {
            return 1;
        } else {
            return c1.compareTo(c2);
        }
}

And then use it when creating the TreeMap:

Map<Character, SomeClass> map = new TreeMap<>(new LowerCaseFirstComaparor());