該代碼可以在Eclipse（20090920-1017）中編譯并正常運(yùn)行import java.util.*;public class SortNull {   static <T extends Comparable<? super T>>   Comparator<T> nullComparableComparator() {      return new Comparator<T>() {         @Override public int compare(T el1, T el2) {         return            el1 == null ? -1 :            el2 == null ? +1 :            el1.compareTo(el2);         }      };   }   public static void main(String[] args) {      List<Integer> numbers = new ArrayList<Integer>(         Arrays.asList(3, 2, 1, null, null, 0)      );      Comparator<Integer> numbersComp = nullComparableComparator();      Collections.sort(numbers, numbersComp);      System.out.println(numbers);      // "[null, null, 0, 1, 2, 3]"      List<String> names = new ArrayList<String>(         Arrays.asList("Bob", null, "Alice", "Carol")      );      Comparator<String> namesComp = nullComparableComparator();      Collections.sort(names, namesComp);      System.out.println(names);      // "[null, Alice, Bob, Carol]"   }}但是它不能在上編譯javac 1.6.0_17。這是錯(cuò)誤消息：SortNull.java:17: incompatible types; no instance(s) of type variable(s) T exist so that java.util.Comparator<T> conforms to java.util.Comparator<java.lang.Integer>found   : <T>java.util.Comparator<T>required: java.util.Comparator<java.lang.Integer>     Comparator<Integer> numbersComp = nullComparableComparator();SortNull.java:25: incompatible types; no instance(s) of type variable(s) T exist so that java.util.Comparator<T> conforms to java.util.Comparator<java.lang.String>found   : <T>java.util.Comparator<T>required: java.util.Comparator<java.lang.String>     Comparator<String> namesComp = nullComparableComparator();2 errors有人可以解釋為什么差異嗎？這是錯(cuò)誤嗎？如果是這樣，誰有錯(cuò)誤？