AddTimes.java

package com.javamultiplex.datetime;

import java.util.Scanner;

/**
 * 
 * @author Rohit Agarwal
 * @category Date and Time
 * @problem How to add two given times in java?
 *
 */
public class AddTimes {

	public static void main(String[] args) {

		Scanner input = null;
		try {
			input = new Scanner(System.in);
			System.out.println("Enter first time(24 hour) in HH:mm:ss format");
			String time1 = input.next();
			System.out.println("Enter second time(24 hour) in HH:mm:ss format");
			String time2 = input.next();
			if (isTimeValid(time1) && isTimeValid(time2)) {

				// Separating first String using delimiter ":"
				String[] firstTimeParts = time1.split(":");
				// Converting String to Integer
				int hours1 = Integer.parseInt(firstTimeParts[0]);
				int minutes1 = Integer.parseInt(firstTimeParts[1]);
				int seconds1 = Integer.parseInt(firstTimeParts[2]);

				// Separating second String using delimiter ":"
				String[] secondTimeParts = time2.split(":");
				// Converting String to Integer
				int hours2 = Integer.parseInt(secondTimeParts[0]);
				int minutes2 = Integer.parseInt(secondTimeParts[1]);
				int seconds2 = Integer.parseInt(secondTimeParts[2]);

				int hours = hours1 + hours2;
				int minutes = minutes1 + minutes2;
				int seconds = seconds1 + seconds2;
				int days = 0;

				/**
				 * 
				 * 60 seconds=1 minute. So if value of seconds>59 adding 1
				 * minute to minutes. 60 minutes=1 hour So if value of
				 * minutes>59 adding 1 hour to hours. 24 hours=1 day So if value
				 * of hours>23 adding 1 day to days.
				 * 
				 */
				if (seconds > 59) {
					seconds = seconds - 60;
					minutes = minutes + 1;
					if (minutes > 59) {
						minutes = minutes - 60;
						hours = hours + 1;
						if (hours > 23) {
							hours = hours - 24;
							days = days + 1;
						}
					} else {

						if (hours > 23) {
							hours = hours - 24;
							days = days + 1;
						}

					}
				} else {
					if (minutes > 59) {
						minutes = minutes - 60;
						hours = hours + 1;
						if (hours > 23) {
							hours = hours - 24;
							days = days + 1;
						}
					} else {

						if (hours > 23) {
							hours = hours - 24;
							days = days + 1;
						}

					}
				}

				// Converting each integer value of String and combining all Strings.
				String finalTime = String.valueOf(days) + ":" + String.valueOf(hours) + ":" + String.valueOf(minutes)
						+ ":" + String.valueOf(seconds);
				System.out.println("New time is :\n" + finalTime);
				System.out.println("OR");
				System.out.println(days + " Days " + hours + " Hours " + minutes + " Minutes " + seconds + " Seconds ");

			} else {
				System.out.println("Time is not valid.");
			}
		} finally {
			if (input != null) {
				input.close();
			}
		}

	}

	private static boolean isTimeValid(String time) {

		boolean result = false;
		/*
		 * Regular expression that matches String with format HH:mm:ss 
		 * HH -> 0-23  
		 * mm -> 0-59 
		 * ss -> 0-59
		 */
		String pattern = "(0?[0-9]|1[0-9]|2[0-3]):(0?[0-9]|[1-5][0-9]):(0?[0-9]|[1-5][0-9])";
		if (time.matches(pattern)) {
			result = true;
		}
		return result;
	}

}