Sorting in java reverseOrder

Here is an example of a custom Comparator method for sorting the way you want:

public class Test {
    public static void main(String[] args) {
        String[] subdivisions = {"K1","K1\\SK1","K2","K2\\SK1\\SSK1"};

        Arrays.stream(subdivisions).sorted(Test::compare).forEach(System.out::println);
    }
    private static int compare(String a, String b) {
        if (a.length() < b.length() && b.startsWith(a))
            return -1; // a is prefix of b, so sort a first
        if (b.length() < a.length() && a.startsWith(b))
            return 1; // b is prefix of a, so sort b first
        return b.compareTo(a); // descending
    }
}

Output

K2
K2\SK1\SSK1
K1
K1\SK1

…here is a lambda expression for the required sorting:

Arrays.stream( subdivisions ).sorted(
    (new Comparator<String>() {
      @Override
      public int compare( String s1, String s2 ) {
        int len = Math.min( s1.length(), s2.length() );
        return( s2.substring( 0, len ).compareTo( s1.substring( 0, len ) ) );
      } }).thenComparing( String::length ) ).forEach( System.out::println );