new TreeSet(comparator) 不带有参数？这是什么意思呃。多谢

import java.util.*; 
public class TreeSetDemo {     
     public static void main(String[] args)
     {              
         Comparator<String> comparator = new CustomComparator1<String>();         
         Set<String> set =   new TreeSet<String>(comparator);                 
         set.add("justin");       
         set.add("caterpillar");         
         set.add("momor");                  
      
         for(String name : set) 
        {             
         System.out.print(name + " ");         
        }         
        System.out.println();     
     }            
 }

import java.util.Comparator;
public class CustomComparator1<T> implements Comparator<T>
{     
           public int compare(T o1, T o2) 
          {         
             if (((T) o1).equals(o2))             
                return 0;         
             return ((Comparable<T>) o1).compareTo((T) o2) * -1;    
          }
}