你如何格式化月份的日期来说“第11”，“第21”或“第23”（序数指标）？

问题

我知道这会给我这个月的日期作为一个数字(11,21,23)：

SimpleDateFormat formatDayOfMonth = new SimpleDateFormat("d");

但是你如何格式化当月的日期，包括anordinal indicator，比如说566198590,21st或23rd？

#1 热门回答(144 赞)

// https://github.com/google/guava
import static com.google.common.base.Preconditions.*;

String getDayOfMonthSuffix(final int n) {
    checkArgument(n >= 1 && n <= 31, "illegal day of month: " + n);
    if (n >= 11 && n <= 13) {
        return "th";
    }
    switch (n % 10) {
        case 1:  return "st";
        case 2:  return "nd";
        case 3:  return "rd";
        default: return "th";
    }
}

来自@kaliatech的表很不错，但由于重复了同样的信息，因此它开启了出错的机会。这个bug实际上存在于表7tn,17tn和27tn中(由于StackOverflow的流畅特性，这个bug可能会随着时间的推移而得到修复，所以checkthe version history on the answer可以看到错误)。

#2 热门回答(47 赞)

JDK中没有任何内容可以做到这一点。

static String[] suffixes =
  //    0     1     2     3     4     5     6     7     8     9
     { "th", "st", "nd", "rd", "th", "th", "th", "th", "th", "th",
  //    10    11    12    13    14    15    16    17    18    19
       "th", "th", "th", "th", "th", "th", "th", "th", "th", "th",
  //    20    21    22    23    24    25    26    27    28    29
       "th", "st", "nd", "rd", "th", "th", "th", "th", "th", "th",
  //    30    31
       "th", "st" };

 Date date = new Date();
 SimpleDateFormat formatDayOfMonth  = new SimpleDateFormat("d");
 int day = Integer.parseInt(formatDateOfMonth.format(date));
 String dayStr = day + suffixes[day];

或使用日历：

Calendar c = Calendar.getInstance();
 c.setTime(date);
 int day = c.get(Calendar.DAY_OF_MONTH);
 String dayStr = day + suffixes[day];

根据@thorbjørn-ravn-andersen的评论，这样的表在本地化时可能会有所帮助：

static String[] suffixes =
     {  "0th",  "1st",  "2nd",  "3rd",  "4th",  "5th",  "6th",  "7th",  "8th",  "9th",
       "10th", "11th", "12th", "13th", "14th", "15th", "16th", "17th", "18th", "19th",
       "20th", "21st", "22nd", "23rd", "24th", "25th", "26th", "27th", "28th", "29th",
       "30th", "31st" };

#3 热门回答(32 赞)

private String getCurrentDateInSpecificFormat(Calendar currentCalDate) {
    String dayNumberSuffix = getDayNumberSuffix(currentCalDate.get(Calendar.DAY_OF_MONTH));
    DateFormat dateFormat = new SimpleDateFormat(" d'" + dayNumberSuffix + "' MMMM yyyy");
    return dateFormat.format(currentCalDate.getTime());
}

private String getDayNumberSuffix(int day) {
    if (day >= 11 && day <= 13) {
        return "th";
    }
    switch (day % 10) {
    case 1:
        return "st";
    case 2:
        return "nd";
    case 3:
        return "rd";
    default:
        return "th";
    }
}