CODEWITHSUNDEEP
javadatetimesubstring
Beef
Beef

Reputation: 1403

convert a string of time to 24 hour format

I have a string holding a start time and an end time in this format 8:30AM - 9:30PM I want to be able to strip out the AM - and the PM and convert all the times to 24 hour format so 9:30PM would really be 21:30 and also have both the times stored in 2 different variables, I know how to strip the string into substrings but Im not sure about the conversion, this is what I have so far. the time variable starts out holding 8:30AM - 9:30PM.

String time = strLine.substring(85, 110).trim();
//time is "8:30AM - 9:30PM" 

String startTime;               
startTime = time.substring(0, 7).trim();
//startTime is "8:30AM"

String endTime;
endTime = time.substring(9).trim();
//endTime "9:30AM"

Upvotes: 5

Views: 35920

Answers (7)

Anonymous
Anonymous

Reputation: 86276

I should like to contribute the modern answer

    DateTimeFormatter twelveHourFormatter = DateTimeFormatter.ofPattern("h:mma", Locale.ENGLISH);

    String time = "8:30AM - 9:30PM";
    String[] times = time.split(" - ");
    LocalTime start = LocalTime.parse(times[0], twelveHourFormatter);
    System.out.println(start.toString());
    LocalTime end = LocalTime.parse(times[1], twelveHourFormatter);
    System.out.println(end.toString());

This prints:

08:30
21:30

I am using java.time, the modern Java date and time API. The SimpleDateFormat class used in many of the other answers is long outdated and was always troublesome. java.time is so much nicer to work with than the date-time classes from the 1990’s. A LocalTime is a time of day without a date (and without time zone), so suits your need much better than an old-fashioned Date.

Link: Oracle tutorial: Date Time explaining how to use java.time.

Upvotes: 2

Ankur Nirmalkar
Ankur Nirmalkar

Reputation: 143

All the below lines will works when String str="07:05:45PM"; and when you call timeConversion(str) and want to convert to 24 hours format..

 public class TimeConversion {

  private static final DateFormat TWELVE_TF = new SimpleDateFormat("hh:mm:ssa");
      private static final DateFormat TWENTY_FOUR_TF = new SimpleDateFormat("HH:mm:ss");


     static String timeConversion(String s) {

         String str = null;
         try {
            str= TWENTY_FOUR_TF.format(
                        TWELVE_TF.parse(s));
        } catch (ParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

         return str;

     }

    public static void main(String[] args) throws ParseException {

        String str="07:05:45PM";

        System.out.println(timeConversion(str));


    }
}

Upvotes: 1

Ed Staub
Ed Staub

Reputation: 15690

With Joda Time, the code looks like:

        DateTimeFormatter formatter12 = DateTimeFormat.forPattern("K:mma");
        DateTime begin = formatter12.parseDateTime(beginTime);
        DateTime end = formatter12.parseDateTime(endTime);

        DateTimeFormatter formatter24 = DateTimeFormat.forPattern("k:mma");
        String begin24 = formatter24.print(begin);
        String end24 = formatter24.print(end);

Upvotes: 2

Anthony Accioly
Anthony Accioly

Reputation: 22461

Working code (considering that you managed to split the Strings):

public class App {
  public static void main(String[] args) {
    try {
        System.out.println(convertTo24HoursFormat("12:00AM")); // 00:00
        System.out.println(convertTo24HoursFormat("12:00PM")); // 12:00
        System.out.println(convertTo24HoursFormat("11:59PM")); // 23:59
        System.out.println(convertTo24HoursFormat("9:30PM"));  // 21:30
    } catch (ParseException ex) {
        Logger.getLogger(App.class.getName()).log(Level.SEVERE, null, ex);
    }
  }
  // Replace with KK:mma if you want 0-11 interval
  private static final DateFormat TWELVE_TF = new SimpleDateFormat("hh:mma");
  // Replace with kk:mm if you want 1-24 interval
  private static final DateFormat TWENTY_FOUR_TF = new SimpleDateFormat("HH:mm");

  public static String convertTo24HoursFormat(String twelveHourTime)
        throws ParseException {
    return TWENTY_FOUR_TF.format(
            TWELVE_TF.parse(twelveHourTime));
  }
}

Now that I think about it, SimpleDateFormat, H h K k can be confusing.

Cheers.

Upvotes: 9

Yevgeny Simkin
Yevgeny Simkin

Reputation: 28349

I wouldn't reinvent the wheel (unless you are doing this as a school project or some such).

Just get a date object out of your time stamp and then you can generate whatever format you want with this: SimpleDateFormat

[edited to address your specific request] if you absolutely need to work from your own unique strings, then you'll do something like this (I don't know exactly what your strings look like... you're using offsets like 85, which means nothing out of context).

I didn't check this for bugs, but this is approximately what you want...

myStr = timestampString.toLowerCase(); //something like 8:30am
boolean add12 = (myStr.indexOf("pm") != -1)?true:false;

//convert hour to int
int hour = Integer.parseInt(myStr.split(":")[0]);

int minutes = Integer.parseInt(  myStr.split(":")[1].replaceAll("\\D+","").replaceAll("^0+","") ); //get the letters out of the minute part and get a number out of that, also, strip out leading zeros

int militaryTime = hour + (add12)? 12:0;
if(!add12 && militaryTime == 12)
 militaryTime = 0; //account for 12am

//dont' forget to add the leading zeros back in as you assemble your string

Upvotes: 3

Todd Moses
Todd Moses

Reputation: 11029

24 hour time adds 12 to any time greater than 12pm so that 1pm is 13 and so on until 24 or 12am. Here is the sudo code:

if(hour <= 12)
{
  hour = hour + 12;
}

Upvotes: 1

zengr
zengr

Reputation: 38899

You need to use: SimpleDateFormat
And can refer this tutorial: Formatting hour using SimpleDateFormat

Example:

//create Date object
Date date = new Date();

//formatting hour in h (1-12 in AM/PM) format like 1, 2..12.
String strDateFormat = "h";
SimpleDateFormat sdf = new SimpleDateFormat(strDateFormat);

System.out.println("hour in h format : " + sdf.format(date));

Upvotes: 4

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