Java Data Type - 如何为枚举值创建比较器

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;

public class Main {
    public static void main(final String[] args) {
        sortDates(Arrays.asList(new DAY[] { DAY.MON, DAY.WED, DAY.TUE, DAY.THU,
                DAY.SUN, DAY.SAT, DAY.FRI }));
    }

    public static void sortDates(final List<DAY> dayList) {
        final Set<DAY> set = new TreeSet<DAY>();
        set.addAll(dayList);
        for (final DAY day : set) {
            System.out.println(day);
        }
    }
}
enum DAY implements Comparable<DAY> {
  MON("MONDAY", 1), TUE("TUESDAY", 2), WED("WEDNESDAY", 3), THU(
          "THURSDAY", 4), FRI("FRIDAY", 5), SAT("SATURDAY", 6), SUN(
          "SUNDAY", 0);

  private String name;
  private int index;

  DAY(String name, int index) {
      name = name;
      index = index;
  }
  public String getName() {
    return name;
  }
  public int getIndex() {
    return index;
  }  
}
class DAYComparator implements Comparator<DAY> {

  @Override
  public int compare(final DAY o1, final DAY o2) {
      int returnValue = 0;
      if (o1.getIndex() > o2.getIndex()) {
          returnValue = 1;
      } else if (o1.getIndex() < o2.getIndex()) {
          returnValue = -1;
      }
      return returnValue;
  }
}