解答例：Calendarクラスの使用
解答例：
Calendar cal = Calendar.getInstance();
int thisYear = cal.get(Calendar.YEAR);
int thisMonth = cal.get(Calendar.MONTH);
int maxDay = cal.getActualMaximum(Calendar.DAY_OF_MONTH);
System.out.println((thisYear) + "年" + (thisMonth+1) +"月は、" + maxDay + "日まであります");
cal.set(thisYear, thisMonth, 1);
int firstDay = cal.get(Calendar.DAY_OF_WEEK);
String[] day = {"---", "日曜日", "月曜日", "火曜日", "水曜日", "木曜日", "金曜日", "土曜日"};
System.out.println((thisYear) + "年" + (thisMonth+1) +"月1日は、" + day[firstDay] + "です");