How to compare Time in java/android (given input in strings)?

I have two strings which are used to store time in the format hh:mm.I want to the compare these two to know which tim开发者_如何学运维e is greater.Which is the easiest way to go about this?

Use the SimpleDateFormat and Date classes. The latter implements Comparable, so you should be able to use the .compareTo() method to do the actual comparison. Example:

            String pattern = "HH:mm";
            SimpleDateFormat sdf = new SimpleDateFormat(pattern);
            try {
                Date date1 = sdf.parse("19:28");
                Date date2 = sdf.parse("21:13");

                // Outputs -1 as date1 is before date2
                System.out.println(date1.compareTo(date2));

                // Outputs 1 as date1 is after date1
                System.out.println(date2.compareTo(date1));

                date2 = sdf.parse("19:28");         
                // Outputs 0 as the dates are now equal
                System.out.println(date1.compareTo(date2));

            } catch (ParseException e){
                // Exception handling goes here
            }

See the SimpleDateFormat documentation for patterns.

Well, if they're actually hh:mm (including leading zeroes, and in 24-hour format) then you can just compare them lexicographically (i.e. using String.compareTo(String)). That's the benefit of a sortable format :)

Of course, that won't check that both values are valid times. If you need to do that, you should probably parse both times: check the length, check the colon, parse two substrings, and probably multiply the number of hours by 60 and add it to the number of minutes to get a total number of minutes. Then you can compare those two totals.

EDIT: As mentioned in the comments, if you do need to parse the values for whatever reason, personally I would recommend using Joda Time (possibly a cut down version, given the mobile nature) rather than SimpleDateTimeFormat and Date. Joda Time is a much nicer date and time API than the built-in one.

I have written functions for this before in my Android program and I will gladly share the source below.

Functions (will explain later using "how to use" code):

public static void String setFormattedTimeString(final String formatExpr,
                                   final long timeStampInSeconds) {     
    final Date dateFromTimeStamp = new Date(timeStampInSeconds);        
    final SimpleDateFormat simpleformat = new SimpleDateFormat(formatExpr);
    final String formattedDateInString = simpleformat.format(dateFromTimeStamp);        
    return formattedDateInString;
}

public static void Calendar setCalendar(final int year, final int month,
                                    final int day) {            
    final Calendar calendar = Calendar.getInstance();           
    calendar.set(Calendar.DAY_OF_MONTH, day);
    calendar.set(Calendar.MONTH, month);
    calendar.set(Calendar.YEAR, year);
    return calendar;            
}

public static void double timeDifferenceInDays(final Calendar firstDate,
                                     final Calendar secondDate) {
    final long firstDateMilli = firstDate.getTimeInMillis();
    final long secondDateMilli = secondDate.getTimeInMillis();
    final long diff = firstDateMilli - secondDateMilli;   

    // 24 * 60 * 60 * 1000 because I want the difference in days. Change
    // as your wish. 
    final double diffDays = (double) diff / (double) (24 * 60 * 60 * 1000);

    return diffDays;
}

And this is how I use them to calculate difference (days in this example). In this example I'm assuming you have a timestamp to use, otherwise you can change easily:

// Here you maybe have a timestamp in seconds or something..    

// This is ONE Calendar.
final String yearString = MyToolClass.setFormattedTimeString("y", timestamp);
final int year = Integer.parseInt(yearString);                                                   
final String monthString = MyToolClass.setFormattedTimeString("M", timestamp);
final int month = Integer.parseInt(monthString);                                      
final String day_in_monthString = MyToolClass.setFormattedTimeString("d",
                                        timestamp);
final int day_of_month = Integer.parseInt(day_in_monthString);

final Calendar calendarOne = MyToolClass.setCalendar(year, month,
                                        day_of_month);   

// Same stuff for Calendar two.

// Calculate difference in days.
final double differenceInDays = MyToolClass.timeDifferenceInDays(calendarOne,
                                        calendarTwo);