How to calculate difference between two times in Java?

Question

I am developing a drug management program and have recorded the last time I used the drug in my database . I want to have the int of time elapsed since the last consumption , for instance int 6 means is 6 hours ago this drug has used

get the time in milliseconds and subtract with current time. — Rajnish suryavanshi, Oct 07 '19 at 14:18
What if the drug was last used 6 hours and 30 minutes ago? How will you store that as an `int` in hour format? — Nexevis, Oct 07 '19 at 14:20
check this https://stackoverflow.com/questions/3514639/android-java-how-to-subtract-two-times — Anas Mehar, Oct 07 '19 at 14:23
I took this occasion for writing [a new and modern answer to the linked original question here](https://stackoverflow.com/a/58280871/5772882). — Ole V.V., Oct 08 '19 at 06:30

score 2 · Accepted Answer · answered Oct 07 '19 at 14:38

You could take two dates/times and minus them from each other to get a duration. This duration can then be converted into whatever format you need.

The example is an example, your mileage may vary.

LocalDateTime fromDateTime = LocalDateTime.of(2019, 10, 07, 7, 45, 55);
LocalDateTime current = LocalDateTime.now();    
long duration = current.toEpochSecond(ZoneOffset.UTC) - fromDateTime.toEpochSecond(ZoneOffset.UTC);
double minutes = duration/60.0;
double hours = duration/3600.0;
System.out.println("Minutes: "+ minutes);
System.out.println("Hours: "+ hours);

Using java.time, the modern Java date and time API, is a good idea. I don’t consider `LocalDateTime` the best suited class in this situation, though. Instead of hand coding the calculation I recommend you let a `Duration` object do the work. Or since only whole hours were asked for, `ChronoUnit.HOURS` is another good option. — Ole V.V., Oct 08 '19 at 12:41

score 1 · Answer 2 · answered Oct 07 '19 at 15:19

This will help you:

public class DateFormatter {

public DateFormatter() {
}

public static Date formatDate(String timestamp) throws ParseException {
    DateFormat dateFormat = new SimpleDateFormat(
            "EEE MMM dd HH:mm:ss zzz yyyy", Locale.US);
    Date date = dateFormat.parse(timestamp);

    return date;
}

/**
 * @param firstDate 
 * @param secondDate 
 * @return firstDate - secondDate in days
 */
public static int dateDaysDifference(Date firstDate, Date secondDate) {
    Long diff = firstDate.getTime() - secondDate.getTime();
    //DecimalFormat decimalFormatter = new DecimalFormat("###,###");
    int diffDays = (int) (diff / (24 * 60 * 60 * 1000));

    diffDays = Math.abs(diffDays);

    return diffDays;
}

/**
 * @param firstDate 
 * @param secondDate 
 * @return firstDate - secondDate in hours
 */
public static int dateHoursDifference(Date firstDate, Date secondDate) {
    Long diff = firstDate.getTime() - secondDate.getTime();
    //DecimalFormat decimalFormatter = new DecimalFormat("###,###");
    int diffhours = (int) (diff / (60 * 60 * 1000));
    //decimalFormatter.format(diffhours);

    diffhours = Math.abs(diffhours);

    return diffhours;
}

/**
 * @param firstDate 
 * @param secondDate 
 * @return firstDate - secondDate in minutes
 */
public static int dateMinDifference(Date firstDate, Date secondDate) {
    Long diff = firstDate.getTime() - secondDate.getTime();
    //DecimalFormat decimalFormatter = new DecimalFormat("###,###");
    int diffmin = (int) (diff / (60 * 1000));
    //decimalFormatter.format(diffmin);

    diffmin = Math.abs(diffmin);
    return diffmin;
}

/**
 * @param firstDate 
 * @param secondDate 
 * @return firstDate - secondDate in seconds
 */
public static int dateSecondDifference(Date firstDate, Date secondDate) {
    Long diff = firstDate.getTime() - secondDate.getTime();
    //DecimalFormat decimalFormatter = new DecimalFormat("###,###");
    int diffsec = (int) (diff / (1000));
    //decimalFormatter.format(diffsec);

    diffsec = Math.abs(diffsec);

    return diffsec;
}

public static void main(String[] args) throws ParseException {
    String timestamp2 = "THU JUL 17 00:15:00 CEST 2013";
    String timestamp = "FRI JUL 15 11:00:00 CEST 2010";
    Date date = formatDate(timestamp);
    Date date2 = formatDate(timestamp2);


    System.out.println("Difference in days: " + dateDaysDifference(date, date2));
    System.out.println("Difference in hours: " + dateHoursDifference(date, date2));
    System.out.println("Difference in minutes: " + dateMinDifference(date, date2));
    System.out.println("Difference in seconds: " + dateSecondDifference(date, date2));
}

}

Please don’t teach the young ones to use the long outdated and notoriously troublesome `SimpleDateFormat` class. At least not as the first option. And not without any reservation. Today we have so much better in [`java.time`, the modern Java date and time API,](https://docs.oracle.com/javase/tutorial/datetime/) and its `DateTimeFormatter`. Yes, you can use it on Android. For older Android see [How to use ThreeTenABP in Android Project](https://stackoverflow.com/questions/38922754/how-to-use-threetenabp-in-android-project). — Ole V.V., Oct 08 '19 at 06:35

How to calculate difference between two times in Java?

2 Answers2