How do I find the difference between two times?

The following code snippet show you how to find the difference between two time objects represented by LocalTime class. To get the difference between two LocalTime objects we can use the Duration.between() method. This method returns a Duration object, to get the difference in seconds we call the getSeconds() method.

Here a code snippet to demonstrate it.

package org.kodejava.example.datetime;

import java.time.*;

public class TimeDifference {
    public static void main(String[] args) {
        LocalTime start = LocalTime.now();
        LocalTime end = LocalTime.of(16, 59, 55);
        Duration duration = Duration.between(start, end);

        System.out.printf("Seconds between %s and %s is: %s seconds.%n",
                start, end, duration.getSeconds());

        diffLocalDateTime();
        diffInstant();
    }

    /**
     * Difference between two LocalDateTime objects.
     */
    public static void diffLocalDateTime() {
        LocalDateTime dt1 = LocalDateTime.now();
        LocalDateTime dt2 = LocalDateTime.now(ZoneId.of("GMT+0"));
        Duration duration = Duration.between(dt1, dt2);
        System.out.printf("Duration = %s seconds.%n", duration.getSeconds());
    }

    /**
     * Difference between two Instant objects.
     */
    public static void diffInstant() {
        Instant instant1 = Instant.now();
        Instant instant2 = Instant.EPOCH;
        Duration duration = Duration.between(instant1, instant2);
        System.out.printf("Duration = %s seconds.%n", duration.getSeconds());
    }
}

Using the Duration.between() we can also get the difference between two LocalDateTime objects and two Instant object as seen in the diffLocalDateTime() method and diffInstant method in the code snippet above.

The result of the code snippet:

Seconds between 16:58:15.863 and 16:59:55 is: 99 seconds.
Duration = -28800 seconds.
Duration = -1455181096 seconds.

How do I format a message that contains time information?

Here we demonstrate how to use the java.text.MessageFormat class to format a message contains a time information.

package org.kodejava.example.text;

import java.util.Date;
import java.util.Calendar;
import java.util.Locale;
import java.text.MessageFormat;

public class MessageFormatTime {
    public static void main(String[] args) {
        Date today = new Date();
        Calendar calendar = Calendar.getInstance();
        calendar.add(Calendar.HOUR, 7);

        Date nextWeek = calendar.getTime();

        // We want the message to be is Locale.US
        Locale.setDefault(Locale.US);

        // Format a time including date information.
        String message = MessageFormat.format("Now is {0} and the next " +
                "7 hours is {1}", today, nextWeek);
        System.out.println(message);

        // Format a time and display only the time portion
        message = MessageFormat.format("Now is {0, time} and the next " +
                "7 hours is {1, time}", today, nextWeek);
        System.out.println(message);

        // Format a time using a short format (eg. HH:mm am/pm)
        message = MessageFormat.format("Now is {0, time, short} and " +
                "the next 7 hours is {1, time, short}", today, nextWeek);
        System.out.println(message);

        // Format a time using a medium format (eg. HH:mm:ss am/pm).
        message = MessageFormat.format("Now is {0, time, medium} and " +
                "the next 7 hours is {1, time, medium}", today, nextWeek);
        System.out.println(message);

        // Format a time using a long format (eg. HH:mm:ss am/pm TIMEZONE).
        message = MessageFormat.format("Now is {0, time, long} and the " +
                "next 7 hours is {1, time, long}", today, nextWeek);
        System.out.println(message);

        // Format a time using a full format (eg. HH:mm:ss am/pm TIMEZONE).
        message = MessageFormat.format("Now is {0, time, full} and the " +
                "next 7 hours is {1, time, full}", today, nextWeek);
        System.out.println(message);

        // Format a time using a custom pattern.
        message = MessageFormat.format("Now is {0, time, HH:mm:ss.sss} " +
                "and the next 7 hours is {1, time, HH:mm:ss.sss}", today, nextWeek);
        System.out.println(message);
    }
}

The above program produces:

Now is 2/15/18, 9:07 PM and the next 7 hours is 2/16/18, 4:07 AM
Now is 9:07:26 PM and the next 7 hours is 4:07:26 AM
Now is 9:07 PM and the next 7 hours is 4:07 AM
Now is 9:07:26 PM and the next 7 hours is 4:07:26 AM
Now is 9:07:26 PM CST and the next 7 hours is 4:07:26 AM CST
Now is 9:07:26 PM China Standard Time and the next 7 hours is 4:07:26 AM China Standard Time
Now is  21:07:26.026 and the next 7 hours is  04:07:26.026

How do I convert string of time to time object?

You want to convert a string representing a time into a time object in Java. As we know that Java represents a time information in a class java.util.Date, this class keep information for date and time.

Now if you have a string of time like 15:30:18, you can use a SimpleDateFormat object to parse the string time and return a java.util.Date object. The pattern of the string should be passed to the SimpleDateFormat constructor. In the example below the string is formatted as hh:mm:ss (hour:minute:second).

package org.kodejava.example.util;

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

public class StringToTimeExample {
    public static void main(String[] args) {        
        // A string of time information
        String time = "15:30:18";

        // Create an instance of SimpleDateFormat with the specified
        // format.
        DateFormat sdf = new SimpleDateFormat("hh:mm:ss");
        try {
            // To get the date object from the string just called the 
            // parse method and pass the time string to it. This method 
            // throws ParseException if the time string is invalid. 
            // But remember as we don't pass the date information this 
            // date object will represent the 1st of january 1970.
            Date date = sdf.parse(time);            
            System.out.println("Date and Time: " + date);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

The code snippet above print the following output:

Date and Time: Thu Jan 01 15:30:18 WITA 1970