public static void main(String[] args) {
    
    Locale.setDefault(Locale.ENGLISH);
    GregorianCalendar d = new GregorianCalendar();
    //現在是當前月份的第幾天
    int today = d.get(Calendar.DAY_OF_MONTH);
    //現在是幾月份
    int month = d.get(Calendar.MONTH);
    //設定當前時間為這個月的第一天
    d.set(Calendar.DAY_OF_MONTH, 1);
    //月份第一天是星期幾
    int weekday = d.get(Calendar.DAY_OF_WEEK);
    //獲取一星期的第一天
    int firstDayOfWeek = d.getFirstDayOfWeek();
    int indent = 0;
    //如果月份的第一個天不是一個星期的第一天，要知道空幾個空格，並把當前時間設定到一星期的第一天
    while (weekday != firstDayOfWeek) {
      indent++;
      d.add(Calendar.DAY_OF_MONTH, -1);
      weekday = d.get(Calendar.DAY_OF_WEEK);
    }

    //列印星期頭
    String[] weekdayNames = new DateFormatSymbols().getShortWeekdays();
    do {
      System.out.printf("%4s", weekdayNames[weekday]);
      d.add(Calendar.DAY_OF_MONTH, 1);
      weekday = d.get(Calendar.DAY_OF_WEEK);
    }
    while (weekday != firstDayOfWeek);
    System.out.println();
    for (int i = 1; i <= indent; i++) {
      System.out.print("    ");
    }
    //設定當前時間為月初
    d.set(Calendar.DAY_OF_MONTH, 1);
    do {
      //列印天數
      int day = d.get(Calendar.DAY_OF_MONTH);
      System.out.printf("%3d", day);

      //標準當前日期
      if (day == today) {
        System.out.print("*");
      } else {
        System.out.print(" ");
      }
      d.add(Calendar.DAY_OF_MONTH, 1);
      weekday = d.get(Calendar.DAY_OF_WEEK);

      //到日期第一天，換行
      if (weekday == firstDayOfWeek){
        System.out.println();
      }
    }
    while (d.get(Calendar.MONTH) == month);
    //最後是否需要換行
    if (weekday != firstDayOfWeek){
      System.out.println();
    }
  }