How to set Time property in Java using Joda-Time

Question

I want to set the hour, minute and seconds in Joda-Time. But when I set it's not changing the property.

Here is my code:

import org.joda.time.DateTime;
public class JodaAkbar 
{
 public static void main(String args[])
 { 
    DateTime dt = new DateTime();
    System.out.println("Before:"+dt);
    dt.hourOfDay().setCopy(5);
    dt.minuteOfDay().setCopy(20);
    dt.secondOfDay().setCopy(0);
    System.out.println("After:"+dt);
 }
}

Here is the output.

Before:2015-04-01T11:01:38.277+11:00
After:2015-04-01T11:01:38.277+11:00

I am getting the same output. What's happening wrong here?

EDIT:

Basically, I want to do something similar as shown in the below code. As the below code doesn't work properly for 24 hour format, I switched to Joda-Time.

 Calendar cal = Calendar.getInstance();
 cal.set(Calendar.HOUR, 13);
 cal.set(Calendar.MINUTE, 25);
 cal.set(Calendar.SECOND, 0);

AKAIK `DateTime` is immutable, it can't be changed in of it self, but `setCopy` will return a new instance of `DateTime` with the update values. `DateTime after = dt.houtOfDay().setCopy(5)`... — MadProgrammer, Apr 01 '15 at 00:13

John Kugelman · Accepted Answer · 2016-03-29T16:03:23.770

Joda-Time objects are immutable. The word "copy" in setCopy is telling you that it doesn't set these fields directly, but instead creates a copy of the DateTime with that field modified.

A quick fix is:

dt = dt.hourOfDay().setCopy(5);
dt = dt.minuteOfHour().setCopy(20);
dt = dt.secondOfMinute().setCopy(0);

A more fluent approach would be to chain several with methods together:

DateTime dt = new DateTime()
    .withHourOfDay(5)
    .withMinuteOfHour(20)
    .withSecondOfMinute(0);

Or do it all with a single withTime call:

DateTime dt = new DateTime().withTime(5, 20, 0, 0);

By the way, Java 8 introduces a new java.time package which was inspired by Joda-Time. The Joda-Time web site recommends, "From Java SE 8 onwards, users are asked to migrate to java.time (JSR-310)."

@MenoHochschild Thanks, I didn't know that. I've rewritten that paragraph. — John Kugelman, Apr 01 '15 at 14:21

score 3 · Answer 2 · answered Apr 01 '15 at 00:13

Look into immutable data structures. The modifiers on a JodaTime object don't really modify the object, but return different instances constructed from the original object with the desired field set as requested.

So, in effect, you're constructing a lot of items, and not assigning them to anything, so they're getting garbage collected. Finally, you're printing out the same (immutable) item twice.

How to set Time property in Java using Joda-Time

2 Answers2