Java Utililty Methods Day of Month

Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
calendar.set(calendar.get(Calendar.YEAR), calendar.get(Calendar.MONTH), 1);
calendar.roll(Calendar.DATE, -1);
return calendar.getTime();

Calendar cal = Calendar.getInstance();
cal.setTime(date);
cal.set(Calendar.DAY_OF_MONTH, cal.getActualMaximum(Calendar.DATE));
return date2String(cal.getTime());

Calendar c = Calendar.getInstance();
c.setTime(date);
c.set(Calendar.DATE, 1);
c.add(Calendar.MONTH, 1);
c.add(Calendar.DATE, -1);
date = c.getTime();
return date;

Calendar c = Calendar.getInstance();
c.setTime(date);
c.set(Calendar.DATE, c.getActualMaximum(Calendar.DAY_OF_MONTH));
return c.getTime();

if (null == dt) {
    return null;
Calendar calendar = Calendar.getInstance();
calendar.setTime(dt);
int day = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
Calendar rtnCalendar = Calendar.getInstance();
rtnCalendar.clear();
...

Calendar cal = Calendar.getInstance();
cal.setTime(firstDate);
return cal.getActualMaximum(Calendar.DATE);

Calendar cal = Calendar.getInstance();
cal.setTime(now);
cal.set(Calendar.DAY_OF_MONTH, 1);
cal.set(Calendar.HOUR_OF_DAY, 23);
cal.set(Calendar.MINUTE, 59);
cal.set(Calendar.SECOND, 59);
cal.set(Calendar.MILLISECOND, 999);
cal.add(Calendar.MONTH, 1);
...

Calendar cDay = Calendar.getInstance();
cDay.setTime(sDate);
int lastDay = cDay.getActualMaximum(Calendar.DAY_OF_MONTH);
Date lastDate = cDay.getTime();
lastDate.setDate(lastDay);
lastDate.setHours(23);
lastDate.setMinutes(59);
lastDate.setSeconds(59);
...

Calendar src = Calendar.getInstance();
src.setTime(date);
Calendar dst = getLastDayOfMonth(src);
return dst.getTime();

Calendar cal = Calendar.getInstance();
int days = 30;
if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12) {
    days = 31;
} else if (month == 2) {
    days = 28;
cal.set(Calendar.DAY_OF_MONTH, days);
...