Java Cookbook

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. Presumably, this is to allow you to print the month name from an array without having to remember to subtract one, but it is 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 PDT 1986 
It is now Sun Jul 18 22:51:47 PDT 1999 
It is now Sun Jul 18 22:51:47 PDT 1999 
D3 set to Mon Apr 12 22:51:47 PDT 1915