我尝试了一个小代码，使用比较排序的学生名单，通过那里的卷号。但我在这行得到编译时错误：

Collections.sort(l);

在我的测试代码下面：

package test;

     import java.util*;

      public class StudentUsingComparator implements
                    Comparator<StudentUsingComparator> {

        int roll;
        String name;

        public StudentUsingComparator(int roll, String name) {
                    this.name = name;
                    this.roll = roll;
        }
        @Override
        public int compare(StudentUsingComparator s1, StudentUsingComparator s2) {
                    return s1.roll - s2.roll;

        }

        public static void main(String[] args) {
                StudentUsingComparator student1 = new StudentUsingComparator(10, "ab");
                StudentUsingComparator student2 = new StudentUsingComparator(30, "cd");
               StudentUsingComparator student3 = new StudentUsingComparator(20, "bc");

              List<StudentUsingComparator> l = new ArrayList<StudentUsingComparator>();
               l.add(student1);
               l.add(student2);
               l.add(student3);
               System.out.println("unsorted collection is:  " + l);
               Collections.sort(l);   //m getting error in this line
               System.out.println("sorted collection is:  " + l);
        }
   }

错误消息显示：
绑定不匹配：集合类型的泛型方法sort（list）不适用于参数list（）。推断类型studentusingcomparator不是有界参数的有效替代品>