How to convert milliseconds to "hh:mm:ss" format?

I'm confused. After stumbling upon this thread, I tried to figure out how to format a countdown timer that had the format hh:mm:ss.

Here's my attempt -

//hh:mm:ss
String.format("%02d:%02d:%02d", 
    TimeUnit.MILLISECONDS.toHours(millis),
    TimeUnit.MILLISECONDS.toMinutes(millis) - 
    TimeUnit.MINUTES.toMinutes(TimeUnit.MILLISECONDS.toHours(millis)),
    TimeUnit.MILLISECONDS.toSeconds(millis) - 
    TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(millis)));

So, when I try a value like 3600000ms, I get 01:59:00, which is wrong since it should be 01:00:00. Obviously there's something wrong with my logic, but at the moment, I cannot see what it is!

Can anyone help?

Edit -

Fixed it. Here's the right way to format milliseconds to hh:mm:ss format -

//hh:mm:ss
String.format("%02d:%02d:%02d", 
    TimeUnit.MILLISECONDS.toHours(millis),
    TimeUnit.MILLISECONDS.toMinutes(millis) - 
    TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS.toHours(millis)),
    TimeUnit.MILLISECONDS.toSeconds(millis) - 
    TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(millis))));

The problem was this TimeUnit.MINUTES.toMinutes(TimeUnit.MILLISECONDS.toHours(millis)). It should have been this TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS.toHours(millis)) instead.

Solution

You were really close:

String.format("%02d:%02d:%02d", 
TimeUnit.MILLISECONDS.toHours(millis),
TimeUnit.MILLISECONDS.toMinutes(millis) -  
TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS.toHours(millis)), // The change is in this line
TimeUnit.MILLISECONDS.toSeconds(millis) - 
TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(millis)));

You were converting hours to millisseconds using minutes instead of hours.

BTW, I like your use of the TimeUnit API :)

Here's some test code:

public static void main(String[] args) throws ParseException {
    long millis = 3600000;
    String hms = String.format("%02d:%02d:%02d", TimeUnit.MILLISECONDS.toHours(millis),
            TimeUnit.MILLISECONDS.toMinutes(millis) - TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS.toHours(millis)),
            TimeUnit.MILLISECONDS.toSeconds(millis) - TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(millis)));
    System.out.println(hms);
}

Output:

01:00:00

I realised that my code above can be greatly simplified by using a modulus division instead of subtraction:

String hms = String.format("%02d:%02d:%02d", TimeUnit.MILLISECONDS.toHours(millis),
    TimeUnit.MILLISECONDS.toMinutes(millis) % TimeUnit.HOURS.toMinutes(1),
    TimeUnit.MILLISECONDS.toSeconds(millis) % TimeUnit.MINUTES.toSeconds(1));

Still using the TimeUnit API for all magic values, and gives exactly the same output.