Convert 24 to 12 Hour and 12 to 24 Hour Time in Java

Time Conversion in Java

In Java, we can easily convert time from 12 to 24 hour and 24 to 12 hour. 

12 hour time 12:00:00 becomes 00:00:00 in 24 hour time. 

Lets jump on code.

Example 1 : Convert 12 Hour to 24 Hour time in Java

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class TimeConversion {

    public static void main(String[] args) {
       
        String s1 = "12:01:00 AM";
        String s2 = "05:30:00 PM";
       
        DateFormat dateFormat = new SimpleDateFormat("hh:mm:ss aa");
        DateFormat outputformat = new SimpleDateFormat("HH:mm:ss");
        try {
            Date date1 = dateFormat.parse(s1);
            Date date2 = dateFormat.parse(s2);
            System.out.println(outputformat.format(date1));
            System.out.println(outputformat.format(date2));
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }

}

Output :

00:01:00
17:30:00

Code Explanation :

We have taken two String time 12 AM and 5:30 PM. First we parse the String time to Date using DateFormat class.

We have to convert 12 to 24 hour time, so another format is set as "HH:mm:ss". 

small hh means 12 hour and capital HH means 24 hour.

Parse the String date to date using DateFormat class reference and store into Date class. Last, print both date to 24 hour format using format() method.

Example 2 : Convert 24 Hour to 12 Hour time in Java

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class TimeConversion {

    public static void main(String[] args) {
        
        String s1 = "00:00:00";
        String s2 = "17:30:00";
        
        DateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");
        DateFormat outputformat = new SimpleDateFormat("hh:mm:ss aa");
        try {
            Date date1 = dateFormat.parse(s1);
            Date date2 = dateFormat.parse(s2);
            
            System.out.println(outputformat.format(date1));
            System.out.println(outputformat.format(date2));
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }

}

Output :

12:00:00 am
05:30:00 pm