java - 使用 Collections.sort 排序列表时出错

Question

当我尝试通过执行 Collections.sort(list2) 对列表进行排序时，出现了 NullPointerException

列表包含以下字符串

[BOOTH 4, ENP ROOM, BOOTH 6, C&T Waiting Area, C&T Waiting Area, C&T Waiting Area, BOOTH 10, BOOTH 7, BOOTH 3, BOOTH 1, C&T Waiting Area, C&T Waiting Area, C&T Waiting Area, C&T Waiting Area, BOOTH 1, C&T Waiting Area, C&T Waiting Area, C&T Waiting Area, C&T Waiting Area, C&T Waiting Area, C&T Waiting Area, C&T Waiting Area, C&T Waiting Area, C&T Waiting Area, BOOTH 10, C&T Waiting Area, C&T Waiting Area, C&T Waiting Area, C&T Waiting Area, C&T Waiting Area, C&T Waiting Area, C&T Waiting Area, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null]

我需要为此列表使用比较器吗？

Answer 1

您可以使用可以处理空值的比较器。例如

private static final class NullsFirstComparator implements Comparator<String> {
  public int compare(String lhs, String rhs) {
    if (lhs == rhs)
      return 0;
    if (lhs == null)
      return -1;
    if (rhs == null)
      return 1;
    return lhs.compareTo(rhs);
  }
}

这将首先对空值进行排序(它们小于所有值)