How to format an elapsed time interval in hh:mm:ss

Question

I'm making a stop watch where I'm using Java's SimpleDateFormat to convert the number of milliseconds into a nice "hh:mm:ss:SSS" format. The problem is the hours field always has some random number in it. Here's the code I'm using:

public static String formatTime(long millis) {
    SimpleDateFormat sdf = new SimpleDateFormat("hh:mm:ss.SSS");

    String strDate = sdf.format(millis);
    return strDate;
}

If I take off the hh part then it works fine. Otherwise in the hh part it'll display something random like "07" even if the argument passed in (number of milliseconds) is zero.

I don't know much about the SimpleDateFormat class though. Thanks for any help.

Answer 1

Here's another way to do it. Fully self-contained and fully backwards-compatible. Unlimited number of days.

private static String slf(double n) {
  return String.valueOf(Double.valueOf(Math.floor(n)).longValue());
}

public static String timeSpan(long timeInMs) {
  double t = Double.valueOf(timeInMs);
  if(t < 1000d)
    return slf(t) + "ms";
  if(t < 60000d)
    return slf(t / 1000d) + "s " +
      slf(t % 1000d) + "ms";
  if(t < 3600000d)
    return slf(t / 60000d) + "m " +
      slf((t % 60000d) / 1000d) + "s " +
      slf(t % 1000d) + "ms";
  if(t < 86400000d)
    return slf(t / 3600000d) + "h " +
      slf((t % 3600000d) / 60000d) + "m " +
      slf((t % 60000d) / 1000d) + "s " +
      slf(t % 1000d) + "ms";
  return slf(t / 86400000d) + "d " +
    slf((t % 86400000d) / 3600000d) + "h " +
    slf((t % 3600000d) / 60000d) + "m " +
    slf((t % 60000d) / 1000d) + "s " +
    slf(t % 1000d) + "ms";
}

Answer 2

Here is what's going on. When you pass milliseconds, that number is relative to Jan 1st, 1970. When you pass 0, it takes that date and converts it to your local time zone. If you are in Central time then that happens to be 7PM. If you run this then it all makes sense.

new SimpleDateFormat().format(0) => 12/31/69 7:00 PM

Edit, I think what you want to do is get elapsed time. For this I recommend using JodaTime which already does this pretty well. You do something like

PeriodFormatter formatter = new PeriodFormatterBuilder()
    .appendHours()
    .appendSuffix(" hour", " hours")
    .appendSeparator(" and ")
    .appendMinutes()
    .appendSuffix(" minute", " minutes")
    .appendSeparator(" and ")
    .appendSeconds()
    .appendSuffix(" second", " seconds")
    .toFormatter();

String formattedText = formatter.print(new Period(elapsedMilliSeconds));

Answer 3

The format happens according to your local timezone, so if you pass 0, it assumes 0 GMT and then converts it in your local timezone.

Answer 4

A shorter way to do this is to use the DurationFormatUtils class in Apache Commons Lang:

public static String formatTime(long millis) {
    return DurationFormatUtils.formatDuration(millis, "HH:mm:ss.S");
}

Answer 5

Here's how I've done it, using only the standard JDK (this will work as far back as Java 1.1 by changing StringBuilder back to StringBuffer):

static public String formatMillis(long val) {
    StringBuilder                       buf=new StringBuilder(20);
    String                              sgn="";

    if(val<0) { sgn="-"; val=Math.abs(val); }

    append(buf,sgn,0,(val/3600000)); val%=3600000;
    append(buf,":",2,(val/  60000)); val%=  60000;
    append(buf,":",2,(val/   1000)); val%=   1000;
    append(buf,".",3,(val        ));
    return buf.toString();
    }

/** Append a right-aligned and zero-padded numeric value to a `StringBuilder`. */
static private void append(StringBuilder tgt, String pfx, int dgt, long val) {
    tgt.append(pfx);
    if(dgt>1) {
        int pad=(dgt-1);
        for(long xa=val; xa>9 && pad>0; xa/=10) { pad--;           }
        for(int  xa=0;   xa<pad;        xa++  ) { tgt.append('0'); }
        }
    tgt.append(val);
    }

Answer 6

This is the first bit of Joda work I've done where it seemed more tedious than the JDK support. A Joda implementation for the requested format (making a few assumptions about zero fields) is:

public void printDuration(long milliSecs)
{
    PeriodFormatter formatter = new PeriodFormatterBuilder()
        .printZeroIfSupported()
        .appendHours()
        .appendSeparator(":")
        .minimumPrintedDigits(2)
        .appendMinutes()
        .appendSeparator(":")
        .appendSecondsWithMillis()
        .toFormatter();

    System.out.println(formatter.print(new Period(milliSecs)));
}