Comparator

import java.util.Comparator;

import my.User;

public class GBComparator implements Comparator{

	public int compare(Object o1, Object o2){
		if(o1 == null){
			return o2 == null ? 0 : 1;
		}
		if(o2 == null){
			return -1;
		}
		
		if(o1 instanceof User && o2 instanceof User){
			return ((User)o1).getAccount().compareTo(((User)o2).getAccount());
		}
		
        return 0;
    }
}