Parsing a Duration String in Kotlin

Question

I\'m working on a Android application and I need to parse a duration string of this form \"00:00:00.000\" (Ex: \"00:00:38.47\" or \"00:03:27.11\").

My final goal is

Answer 1

java.time.Duration

As shown in the linked questions there are several ways to do this. I am afraid that there isn’t one objectively best way.

You should most probably use a Duration from java.time, the modern Java date and time API, for your duration.

Unfortunately there isn’t a way to parse your string directly into a Duration. My preference is for modifying your string into ISO 8601 format, the format that the Duration class knows how to parse. I trust you to translate my Java code into even more beautiful Kotlin code.

    String timeString = "00:01:08.83";
    String isoDurationString = timeString
            .replaceFirst("(\\d+):(\\d{2}):(\\d{2}(?:\\.\\d+)?)", "PT$1H$2M$3S");
    Duration dur = Duration.parse(isoDurationString);
    System.out.println(dur);

Output from this snippet is:

PT1M8.83S

The regular expression is powerful but hard to read. The round brackets denote groups that I want to keep in the modified string; I refer to them as $1 etc. in the replacement string. (?:\\.\\d+) is a non-capturing group, one that I don’t need to use in the replacement. The ? after the non-capturing group says that it needs not be there (so the expression matches just 00:01:08 as well).

For a percentage there are some options again. Duration objects can be directly multiplied by 100 and since Java 9 divided by each other. Assuming that you are not yet on Java 9, I would probably make the calculation based on milliseconds or nanoseconds (rather than seconds with a fraction). For example:

    long totalMilliseconds = dur.toMillis();
    System.out.println(totalMilliseconds);

68830

However to answer your question here’s how I would convert to seconds in a float:

    float totalSeconds = ((float) dur.toNanos()) / TimeUnit.SECONDS.toNanos(1);
    System.out.println(totalSeconds);

68.83