[java] How to set time to 24 hour format in Calendar

I need to set the time on the current date. The time string is always in 24 hour format but the result I get is wrong:

  SimpleDateFormat df = new SimpleDateFormat("kk:mm");
  Date d1 = df.parse("10:30");
  Calendar c1 = Calendar.getInstance();
  c1.set(Calendar.HOUR, d1.getHours());
  c1.set(Calendar.MINUTE, d1.getMinutes());

The date should be today's date and the time set to 10:30. Instead the time in c1 ends up being 22:30. How can I force the calendar control to recognize my time is 24 hour format?

EDIT: If I just do this:

Calendar c1 = Calendar.getInstance();
c1.set(Calendar.HOUR, 10);
c1.set(Calendar.MINUTE, 30);

This gives me the same result. Why?

tl;dr

LocalTime.parse( "10:30" )  // Parsed as 24-hour time.

java.time

Avoid the troublesome old date-time classes such as Date and Calendar that are now supplanted by the java.time classes.

LocalTime

The java.time classes provide a way to represent the time-of-day without a date and without a time zone: LocalTime

LocalTime lt = LocalTime.of( 10 , 30 );  // 10:30 AM.
LocalTime lt = LocalTime.of( 22 , 30 );  // 22:30 is 10:30 PM.

ISO 8601

The java.time classes use standard ISO 8601 formats by default when generating and parsing strings. These formats use 24-hour time.

String output = lt.toString();

LocalTime.of( 10 , 30 ).toString() : 10:30

LocalTime.of( 22 , 30 ).toString() : 22:30

So parsing 10:30 will be interpreted as 10:30 AM.

LocalTime lt = LocalTime.parse( "10:30" );  // 10:30 AM.

DateTimeFormatter

If you need to generate or parse strings in 12-hour click format with AM/PM, use the DateTimeFormatter class. Tip: make a habit of specifying a Locale.

Try this :

SimpleDateFormat df = new SimpleDateFormat("hh:mm");

Or

SimpleDateFormat df = new SimpleDateFormat("KK:mm");

Reference : SimpleDateFormat

private void setClock() {

    Timeline clock = new Timeline(new KeyFrame(Duration.ZERO, e -> {
        Calendar cal = Calendar.getInstance();
        int second = cal.get(Calendar.SECOND);
        int minute = cal.get(Calendar.MINUTE);
        int  hour = cal.get(Calendar.HOUR_OF_DAY);
        eski_minut = minute;
        if(second < 10){

            time_label.setText(hour + ":" + (minute) + ":0" + second);

        }else if (minute < 10){
            time_label.setText(hour + ":0" + (minute) + ":0" + second);

        }
        else {
        time_label.setText(hour + ":" + (minute) + ":" + second);}
    }),
            new KeyFrame(Duration.seconds(1))
    );
    clock.setCycleCount(Animation.INDEFINITE);
    clock.play();
}

Replace this:

c1.set(Calendar.HOUR, d1.getHours());

with this:

c1.set(Calendar.HOUR_OF_DAY, d1.getHours());

Calendar.HOUR is strictly for 12 hours.

Here you will get all kinds of time related problems. I hope this will solve your problem.

public class MyClass {

    public static void main(String[] args) {


        Calendar cal = Calendar.getInstance();

        // To get the current hour
        int hour = cal.get(Calendar.HOUR_OF_DAY);
        System.out.println("hour: " + hour);

        // To get the current time in 12 hours format
        SimpleDateFormat sdf = new SimpleDateFormat("hh:mm a",Locale.US);
        String a = sdf.format(cal.getTime());
        System.out.println("Time: " + a);

        // To get the desired time in 12 hours format from 23 hours format
        cal.set(Calendar.HOUR_OF_DAY, 24);
        SimpleDateFormat sdf1 = new SimpleDateFormat("hh:mm a",Locale.ENGLISH);
        String a1 = sdf1.format(cal.getTime());
        System.out.println("Time: " + a1);

        /*  H Hour in day (0-23) 
            k Hour in day (1-24) 
        */

        //To get the desired time in 24 hours format as 0-23 or 1-24
        cal.set(Calendar.HOUR_OF_DAY, 24);
        SimpleDateFormat sdf2 = new SimpleDateFormat("HH:mm",Locale.ENGLISH);
        SimpleDateFormat sdf3 = new SimpleDateFormat("kk:mm",Locale.ENGLISH);
        String a2 = sdf2.format(cal.getTime());
        String a3 = sdf3.format(cal.getTime());
        System.out.println("Time: " + a2);
        System.out.println("Time: " + a3);

        //For example, time like 12:30 PM. How can i convert to 24 hours time in java?

        SimpleDateFormat bigFormat = new SimpleDateFormat("kk:mm");
        SimpleDateFormat smallFormat = new SimpleDateFormat("hh:mm a");

        Date date = null;
        try {
            date = smallFormat.parse("12:30 AM");
        } catch (ParseException e) {
            e.printStackTrace();
        }        
        System.out.println(smallFormat.format(date) + " = " + bigFormat.format(date));

    }

}

if you replace in the function SimpleDateFormat("hh") with ("HH") will format the hour in 24 hours instead of 12.

SimpleDateFormat df = new SimpleDateFormat("HH:mm");

use SimpleDateFormat df = new SimpleDateFormat("HH:mm"); instead

UPDATE

@Ingo is right. is's better use setTime(d1);

first method getHours() and getMinutes() is now deprecated

I test this code

SimpleDateFormat df = new SimpleDateFormat("hh:mm");
  Date d1 = df.parse("23:30");
  Calendar c1 = GregorianCalendar.getInstance();
  c1.setTime(d1);
  System.out.println(c1.getTime());

and output is ok Thu Jan 01 23:30:00 FET 1970

try this

SimpleDateFormat df = new SimpleDateFormat("KK:mm aa");
  Date d1 = df.parse("10:30 PM");
  Calendar c1 = GregorianCalendar.getInstance(Locale.US);
  SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");  
  c1.setTime(d1);
  String str = sdf.format(c1.getTime());
  System.out.println(str);

I am using fullcalendar on my project recently, I don't know what exact view effect you want to achieve, in my project I want to change the event time view from 12h format from

to 24h format.

If this is the effect you want to achieve, the solution below might help:

set timeFormat: 'H:mm'

You can set the calendar to use only AM or PM using

calendar.set(Calendar.AM_PM, int);

0 = AM

1 = PM

Hope this helps