How to get hour value in 24 hour format

Calendar calendar = Calendar.getInstance();
System.out.println(calendar.get(Calendar.HOUR_OF_DAY)); // print hour in 24 format

Java Calendar - Calendar.MONTH is zero-based

Calendar calendar = Calendar.getInstance();
calendar.set(2010, 4, 10);
System.out.println(calendar.getActualMaximum(Calendar.DAY_OF_MONTH));
System.out.println(calendar.get(Calendar.DAY_OF_MONTH));

It's weird thing calendar.set(2010, 4, 10), actually set date as May 10, 2010. "4" for the MONTH field is really misleading. It sets Month as "May".

caalendar.getActualMaximum() calculates the maximum of days in month of May.

So output should be:
31
10

Java Date Format and Current Date Time

DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
Date date = new Date();
System.out.println(dateFormat.format(date));

DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
Calendar cal = Calendar.getInstance();
System.out.println(dateFormat.format(cal.getTime()));