Writing Own Custom Comparator In Java

I have a java code that should sort an array of names based on the last name. e.g jane a, jane b, jane z, jane d should be jane a, jane b, jane d, jane z. I have the following code but for some reasons, the s1 in the comparator method is always null.
 
public class ShuffleName {
public static void sortNames(String[] names){
 Arrays.sort( names, new Comparator<String>() {
 public int compare( String s1, String s2 ) { 
String s1last = s1.split("s+")[1];
String s2last = s2.split("s+")[1];
return s1last.compareTo(s2last);

[code]....