这里有一个getter：

public boolean isFirstDayofMonth(Calendar calendar){
    if (calendar == null) {
        throw new IllegalArgumentException("Calendar cannot be null.");
    }

    int dayOfMonth = calendar.get(Calendar.DAY_OF_MONTH);
    return dayOfMonth == 1;
}

使用LocalDate和TemporalAdjuster的Java 8解决方案

每月第一天：

someDate.isEqual(someDate.with(firstDayOfMonth()))

每月最后一天：

someDate.isEqual(someDate.with(lastDayOfMonth())

此解决方案使用java.time.temporal中的TemporalAdjusters实用程序。通常将其用作import static，但您也可以将其用作TemporalAdjusters.lastDayOfMonth()

public static boolean isFirstDayOfTheMonth(Date dateToday){
    Calendar cal = Calendar.getInstance();
    c.setTime(dateToday );

    if (c.get(Calendar.DAY_OF_MONTH) == 1) {
      return true;
    }
    return false;
}