Start and end date of a current month

There you go:

public Pair<Date, Date> getDateRange() {
    Date begining, end;

    {
        Calendar calendar = getCalendarForNow();
        calendar.set(Calendar.DAY_OF_MONTH,
                calendar.getActualMinimum(Calendar.DAY_OF_MONTH));
        setTimeToBeginningOfDay(calendar);
        begining = calendar.getTime();
    }

    {
        Calendar calendar = getCalendarForNow();
        calendar.set(Calendar.DAY_OF_MONTH,
                calendar.getActualMaximum(Calendar.DAY_OF_MONTH));
        setTimeToEndofDay(calendar);
        end = calendar.getTime();
    }

    return Pair.of(begining, end);
}

private static Calendar getCalendarForNow() {
    Calendar calendar = GregorianCalendar.getInstance();
    calendar.setTime(new Date());
    return calendar;
}

private static void setTimeToBeginningOfDay(Calendar calendar) {
    calendar.set(Calendar.HOUR_OF_DAY, 0);
    calendar.set(Calendar.MINUTE, 0);
    calendar.set(Calendar.SECOND, 0);
    calendar.set(Calendar.MILLISECOND, 0);
}

private static void setTimeToEndofDay(Calendar calendar) {
    calendar.set(Calendar.HOUR_OF_DAY, 23);
    calendar.set(Calendar.MINUTE, 59);
    calendar.set(Calendar.SECOND, 59);
    calendar.set(Calendar.MILLISECOND, 999);
}

PS: Pair class is simply a pair of two values.

If you have the option, you'd better avoid the horrid Java Date API, and use instead Jodatime (or equivalently the Java 8 java.time.* API). Here is an example:

LocalDate monthBegin = new LocalDate().withDayOfMonth(1);
LocalDate monthEnd = new LocalDate().plusMonths(1).withDayOfMonth(1).minusDays(1);