Java Converting YMDHMS to a Calendar or Epoch Seconds

Java Converting YMDHMS to a Calendar

or Epoch Seconds

Problem

You have year, month, day, hour, minute, and maybe even seconds, and you need to
convert it to a Calendar or a Date .

Solution

Use the Calendar class’s set(y,m,d,h,m[,s]) method, which allows you to set the
date/time fields to whatever you wish. Note that when using this form and providing
your own numbers, or when constructing either a Date or a GregorianCalendar
object, the month value is zero-based while all the other values are true-origin. Pre-
sumably, this is to allow you to print the month name from an array without having
to remember to subtract one, but it is still confusing.

// GregCalDemo.java
GregorianCalendar d1 = new GregorianCalendar(1986, 04, 05); // May 5
GregorianCalendar d2 = new GregorianCalendar( );
// today
Calendar d3 = Calendar.getInstance( );
// today
System.out.println("It was then " + d1.getTime( ));
System.out.println("It is now " + d2.getTime( ));
System.out.println("It is now " + d3.getTime( ));
d3.set(Calendar.YEAR, 1915);
d3.set(Calendar.MONTH, Calendar.APRIL);
d3.set(Calendar.DAY_OF_MONTH, 12);
System.out.println("D3 set to " + d3.getTime( ));

This prints the dates as shown:

It was then Mon May 05 00:00:00 EDT 1986
It is now Thu Mar 25 16:36:07 EST 2004
It is now Thu Mar 25 16:36:07 EST 2004
D3 set to Mon Apr 12 16:36:07 EST 1915