Develop Reference

Totalling times in HHMM format

So i have a series of times:
ArrayList<String> times = new ArrayList<String>();
times.add("1240");
times.add("1028");
times.add("0923");
times.add("2023");
And I wan't to find the total hours traversed between these times, but I can't figure out how!
For example:
"1240 to 1028" would be 11hrs20 + 10hrs28 in travel time.
To go from 12h40 on one day to 10h28 next day, you need 11h20 (going to midnight), then 10h28. Quite clear.

First we need a way to convert a string into a linear time representation:
// Given a string of the form HHMM, this returns the number of minutes after midnight.
// For example: timeStringToMinutes("0000") -> 0.
// timeStringToMinutes("0015") -> 15.
// timeStringToMinutes("0100") -> 60.
// timeStringToMinutes("0837") -> 517.
// timeStringToMinutes("2359") -> 1439.
static int timeStringToMinutes(String s) {
return Integer.parseInt(s.substring(0, 2)) * 60 + Integer.parseInt(s.substring(2, 4));
}
Next we define a function to compute time differences:
// Example: forwardNumberOfMinutes("1240", "1028") -> 1308.
static int forwardNumberOfMinutes(String start, String end) {
int from = timeStringToMinutes(start);
int to = timeStringToMinutes(end);
if (to < from)
to += 1440; // 1 day, or 24 hours
return to - from;
}
Finally we define a function to convert linear time to hours and minutes:
// Example: minutesToTimeString(1308) -> "2148" (21 hr 48 min).
static minutesToTimeString(int n) {
return String.format("%02d%02d", n / 60, n % 60);
}

time difference in military time in Java

So for an assignment we had to write a program that takes two times in military time and shows the difference in hours and minutes between them assuming the first time is the earlier of the two times. We weren't allowed to use if statements as it technically has not be learned. Here's an example of what it'd look like run. In quotes I'll put what is manually entered when it is prompted to.
java MilitaryTime
Please enter first time: "0900"
Please enter second time: "1730"
8 hours 30 minutes (this is the final answer)
I was able to quite easily get this part done with the following code:
class MilitaryTime {
public static void main(String [] args) {
Scanner in = new Scanner(System.in);
System.out.println("Please enter the first time: ");
int FirstTime = in.nextInt();
System.out.println("Please enter the second time: ");
int SecondTime = in.nextInt();
int FirstHour = FirstTime / 100;
int FirstMinute = FirstTime % 100;
int SecondHour = SecondTime / 100;
int SecondMinute = SecondTime % 100;
System.out.println( ( SecondHour - FirstHour ) + " hours " + ( SecondMinute
- FirstMinute ) + " minutes " );
}
}
Now my question is something wasn't assigned (or I wouldn't be here!) is there's another part to this question in the book that says to take that program we just wrote and deal with the case where the first time is later than the second. This has really intrigued me about how this would be done and has really stumped me. Again we aren't allowed to use if statements or this would be easy we basically have all the mathematical functions to work with.
An example would be the first time is now 1730 and the second time is 0900 and so now it returns 15 hours 30 minutes.

I would like to suggest to use org.joda.time.DateTime. There are a lot of date and time functions.
Example :
SimpleDateFormat format = new SimpleDateFormat("dd-MM-yyyy hh:mm");
Date startDate = format.parse("10-05-2013 09:00");
Date endDate = format.parse("11-05-2013 17:30");
DateTime jdStartDate = new DateTime(startDate);
DateTime jdEndDate = new DateTime(endDate);
int years = Years.yearsBetween(jdStartDate, jdEndDate).getYears();
int days = Days.daysBetween(jdStartDate, jdEndDate).getDays();
int months = Months.monthsBetween(jdStartDate, jdEndDate).getMonths();
int hours = Hours.hoursBetween(jdStartDate, jdEndDate).getHours();
int minutes = Minutes.minutesBetween(jdStartDate, jdEndDate).getMinutes();
System.out.println(hours + " hours " + minutes + " minutes");
Your expected program will be as below :
SimpleDateFormat format = new SimpleDateFormat("hhmm");
Dates tartDate = format.parse("0900");
Date endDate = format.parse("1730");
DateTime jdStartDate = new DateTime(startDate);
DateTime jdEndDate = new DateTime(endDate);
int hours = Hours.hoursBetween(jdStartDate, jdEndDate).getHours();
int minutes = Minutes.minutesBetween(jdStartDate, jdEndDate).getMinutes();
minutes = minutes % 60;
System.out.println(hours + " hours " + minutes + " minutes");
Output :
8 hours 30 minutes

Normally, when dealing with time calculations of this nature I would use Joda-Time, but assuming that you don't care about the date component and aren't rolling over the day boundaries, you could simply convert the value to minutes or seconds since midnight...
Basically the problem you have is the simple fact that there are 60 minutes in an hour, this makes doing simple mathematics impossible, you need something which is more common
For example, 0130 is actually 90 minutes since midnight, 1730 is 1050 minutes since midnight, which makes it 16 hours in difference. You can simply subtract the two values to get the difference, then convert that back to hours and minutes...for example...
public class MilTimeDif {
public static void main(String[] args) {
int startTime = 130;
int endTime = 1730;
int startMinutes = minutesSinceMidnight(startTime);
int endMinutes = minutesSinceMidnight(endTime);
System.out.println(startTime + " (" + startMinutes + ")");
System.out.println(endTime + " (" + endMinutes + ")");
int dif = endMinutes - startMinutes;
int hour = dif / 60;
int min = dif % 60;
System.out.println(hour + ":" + min);
}
public static int minutesSinceMidnight(int milTime) {
double time = milTime / 100d;
int hours = (int) Math.floor(time);
int minutes = milTime % 100;
System.out.println(hours + ":" + minutes);
return (hours * 60) + minutes;
}
}
Once you start including the date component or rolling over day boundaries, get Joda-Time out

I would do something like:
System.out.println(Math.abs( SecondHour - FirstHour ) + " hours " + Math.abs( SecondMinute - FirstMinute ) + " minutes " );
The absolute value will give you the difference between the two times as a positive integer.

You could do something like this
//Code like you already have
System.out.println("Please enter the first time: ");
int firstTime = in.nextInt();
System.out.println("Please enter the second time: ");
int secondTime = in.nextInt();
//Now we can continue using the code you already wrote by
//forcing the smaller of the two times into the 'firstTime' variable.
//This forces the problem to be the same situation as you had to start with
if (secondTime < firstTime) {
int temp = firstTime;
firstTime = secondTime;
secondTime = temp;
}
//Continue what you already wrote
There are many other ways but this was something I used for similar problems while learning. Also, note that I changed variable names to follow java naming conventions - variables are lowerCamelCase.

I used 3 classes. Lets go over theory first.
We have two times: A and B.
if AtimeDiff = (B-A).....which can be written -(A-B)
if A>B, then timeDiff = 1440- (A-B) [1440 is total minutes in day]
Thus we need to make timeDiff = 1440 - (A-B) and we need to make 1440 term dissapear when A
Lets make a term X = (A-B+1440) / 1440 (notice "/" is integer division.
'if A
'if A>B then X = 1;
Now look at a new term Y = 1440 * X.
'if A
'if A>B then Y = 1440'.
PROBLEM SOLVED. Now just plug into Java Programs. Note what happens if A=B. Our program will assume we know no time passes if times are exact same time. It assumes that 24 hours have passed. Anyways check out the 3 programs listed below:
Class #1
public class MilitaryTime {
/**
* MilitaryTime A time has a certain number of minutes passed at
* certain time of day.
* #param milTime The time in military format
*/
public MilitaryTime(String milTime){
int hours = Integer.parseInt(milTime.substring(0,2));
int minutes = Integer.parseInt(milTime.substring(2,4));
timeTotalMinutes = hours * 60 + minutes;
}
/**
* Gets total minutes of a Military Time
* #return gets total minutes in day at certain time
*/
public int getMinutes(){
return timeTotalMinutes;
}
private int timeTotalMinutes;
}
Class#2
public class TimeInterval {
/**
A Time Interval is amount of time that has passed between two times
#param timeA first time
#param timeB second time
*/
public TimeInterval(MilitaryTime timeA, MilitaryTime timeB){
// A will be shorthand for timeA and B for timeB
// Notice if A<B timeDifferential = TOTAL_MINUTES_IN_DAY - (A - B)
// Notice if A>B timeDifferential = - (A - B)
// Both will use timeDifferential = TOTAL_MINUTES_IN_DAY - (A - B),
// but we need to make TOTAL_MINUTES_IN_DAY dissapear when needed
//Notice A<B following term "x" is 1 and if A>B then it is 0.
int x = (timeA.getMinutes()-timeB.getMinutes()+TOTAL_MINUTES_IN_DAY)
/TOTAL_MINUTES_IN_DAY;
// Notice if A<B then term "y" is TOTAL_MINUTES_IN_DAY(1440 min)
// and if A<B it is 0
int y = TOTAL_MINUTES_IN_DAY * x;
//yay our TOTAL_MINUTES_IN_DAY dissapears when needed.
int timeDifferential = y - (timeA.getMinutes() - timeB.getMinutes());
hours = timeDifferential / 60;
minutes = timeDifferential % 60;
//Notice that if both hours are equal, 24 hours will be shown.
// I assumed that we would knoe if something start at same time it
// would be "0" hours passed
}
/**
* Gets hours passed between 2 times
* #return hours of time difference
*/
public int getHours(){
return hours;
}
/**
* Gets minutes passed after hours accounted for
* #return minutes remainder left after hours accounted for
*/
public int getMinutes(){
return minutes;
}
private int hours;
private int minutes;
public static final int TOTAL_MINUTES_IN_DAY = 1440;//60minutes in 24 hours
}
Class#3
import java.util.Scanner;
public class MilitaryTimeTester {
public static void main (String[] args){
Scanner in = new Scanner(System.in);
System.out.println("Enter time A: ");
MilitaryTime timeA = new MilitaryTime(in.nextLine());
System.out.println("Enter time B: ");
MilitaryTime timeB = new MilitaryTime(in.nextLine());
TimeInterval intFromA2B = new TimeInterval(timeA,timeB);
System.out.println("Its been "+intFromA2B.getHours()+" hours and "+intFromA2B.getMinutes()+" minutes.");
}
}

import java.util.Scanner;
public class TimeDifference{
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
// read first time
System.out.println("Please enter the first time: ");
int firstTime = in.nextInt();
// read second time
System.out.println("Please enter the second time: ");
int secondTime = in.nextInt();
in.close();
// if first time is more than second time, then the second time is in
// the next day ( + 24 hours)
if (firstTime > secondTime)
secondTime += 2400;
// first hour & first minutes
int firstHour = firstTime / 100;
int firstMinute = firstTime % 100;
// second hour & second minutes
int secondHour = secondTime / 100;
int secondMinute = secondTime % 100;
// time difference
int hourDiff = secondHour - firstHour;
int minutesDiff = secondMinute - firstMinute;
// adjust negative minutes
if (minutesDiff < 0) {
minutesDiff += 60;
hourDiff--;
}
// print out the result
System.out.println(hourDiff + " hours " + minutesDiff + " minutes ");
}
}

This one is done without using ifs and date thingy. you just need to use integer division "/", integer remainder thing"%", and absolute value and celing. might be able to be simplified but im too lazy at moment. I struggled for hours to figure out and seems nobody else got the answer without using more advanced functions. this problem was in Cay Horstmann's Java book. Chapter 4 in Java 5-6 version of the book "Java Concepts"
import java.util.Scanner;
public class MilitaryTime {
public static void main (String[] args){
//creates input object
Scanner in = new Scanner(System.in);
System.out.println("Enter time A: ");
String timeA = in.next();
System.out.println("Enter time B: ");
String timeB = in.next();
//Gets the hours and minutes of timeA
int aHours = Integer.parseInt(timeA.substring(0,2));
int aMinutes = Integer.parseInt(timeA.substring(2,4));
//Gets the hours and minutes of timeB
int bHours = Integer.parseInt(timeB.substring(0,2));
int bMinutes = Integer.parseInt(timeB.substring(2,4));
//calculates total minutes for each time
int aTotalMinutes = aHours * 60 + aMinutes;
int bTotalMinutes = bHours * 60 + bMinutes;
//timeA>timeB: solution = (1440minutes - (aTotalMinutes - bTotalMinutes))
//timeA<timeB: solution is (bTotalMinutes - aTotalMinutes) or
//-(aTotalMinutes - bTotalMinutes)
//we need 1440 term when timea>timeeB... we use mod and mod remainder
//decider is 1 if timeA>timeB and 0 if opposite.
int decider = ((aTotalMinutes - bTotalMinutes +1440)/1440);
// used 4 Special case when times are equal. this way we get 0
// timeDiffference term when equal and 1 otherwise.
int equalsDecider = (int) Math.abs((aTotalMinutes - bTotalMinutes));
//fullDayMaker is used to add the 1440 term when timeA>timeB
int fullDayMaker = 1440 * decider;
int timeDifference = (equalsDecider)* (fullDayMaker - (aTotalMinutes - bTotalMinutes));
// I convert back to hours and minmutes using modulater
System.out.println(timeDifference/60+" hours and "+timeDifference%60+" minutes");
}
}

java.time
Java 8 and later includes the new java.time framework. See the Tutorial.
The new classes include LocalTime for representing a time-only value without date and without time zone.
Another class is Duration, for representing a span of time as a total number of seconds and nanoseconds. A Duration may be viewed as a number of hours and minutes.
By default the Duration class implements the toString method to generate a String representation of the value using the ISO 8601 format of PnYnMnDTnHnMnS where the P marks the beginning and the T separates the date portion from the time portion. The Duration class can parse as well as generate strings in this standard format.
So, the result in example code below is PT8H30M for eight and a half hours. This format is more sensible than 08:30 which can so easily be confused for a time rather than a duration.
String inputStart = "0900";
String inputStop = "1730";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern ( "HHmm" );;
LocalTime start = formatter.parse ( inputStart , LocalTime :: from );
LocalTime stop = formatter.parse ( inputStop , LocalTime :: from );
Duration duration = Duration.between ( start , stop );
Dump to console.
System.out.println ( "From start: " + start + " to stop: " + stop + " = " + duration );
When run.
From start: 09:00 to stop: 17:30 = PT8H30M

import java.util.*;
class Time
{
static Scanner in=new Scanner(System.in);
public static void main(String[] args)
{
int time1,time2,totalTime;
System.out.println("Enter the first time in military:");
time1=in.nextInt();
System.out.println("Enter the second time in military:");
time2=in.nextInt();
totalTime=time2-time1;
String temp=Integer.toString(totalTime);
char hour=temp.charAt(0);
String min=temp.substring(1,3);
System.out.println(hour+" hours "+min+" minutes");
}
}

Find average of time in (hh mm ss) format in java

I want to Calculate the average of three time in hh:mm:ss format . I tried the following code .
public String calculateAverageOfTime()
{
String timeInHHmmss = "08:00:00 08:00:00 08:00:00";
String[] split = timeInHHmmss.split(" ");
long hh = 0,mm = 0,ss = 0;
for (int i = 0; i < split.length; i++)
{
String[] split1 = split[i].split(":");
hh += Long.valueOf(split1[0].trim());
mm += Long.valueOf(split1[1].trim());
ss += Long.valueOf(split1[2].trim());
}
hh = hh / split.length ;
mm = mm / split.length ;
ss = ss / split.length ;
String hms = String.format("%02d:%02d:%02d", hh,mm,ss);
return hms;
}
This code works well. Is there any efficient way to do this ? . Any method available in Java API .

Your current code is not correct, try for example with input 08:00:00 08:00:00 09:30:00. As #StephenC said it, you cannot average times by averaging hour, minute, second components. Times are like base-60 numbers, you know, 60 seconds + 1 = 1:00 instead of 61.
This is correct, calculating the sum of seconds, then taking average and converting back to time:
public static String calculateAverageOfTime(String timeInHHmmss) {
String[] split = timeInHHmmss.split(" ");
long seconds = 0;
for (String timestr : split) {
String[] hhmmss = timestr.split(":");
seconds += Integer.valueOf(hhmmss[0]) * 60 * 60;
seconds += Integer.valueOf(hhmmss[1]) * 60;
seconds += Integer.valueOf(hhmmss[2]);
}
seconds /= split.length;
long hh = seconds / 60 / 60;
long mm = (seconds / 60) % 60;
long ss = seconds % 60;
return String.format("%02d:%02d:%02d", hh,mm,ss);
}
Using Date, SimpleDateFormat or Joda would make the code easier to understand, but I don't think it can be more efficient than this, as this code does strictly what you want to do, which is averaging a base-60 number.
As others have pointed out, beware of the precision loss when averaging.
You might also want to validate that the input string is in the correct format, otherwise the algorithm will break.

There is no single method in the Java API that will solve this problem. But there are some that will help.
What you need to do is to break the problem down into parts:
Convert time strings to numbers.
Average the numbers
Convert the average back to a time string.
The problems of converting a time string to a number and a number to a time string can be solved using the SimpleDateFormat class, or the 3rd-party Joda time class library. Or you could manually extract the hours/minutes/seconds component, convert each to an integer and then compute the number of seconds.
The problem of averaging 3 numbers can be solved with one line of Java ... though you need to beware of the fact that integer division truncates the result.
For the record, you cannot average 3 times by averaging their three components, as you current code tries to do. It doesn't make mathematical sense.

Something like this should work:
String timeInHHmmss = "08:00:00 08:00:00 08:00:00";
String[] split = timeInHHmmss.split(" ");
long sum = 0L;
SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");
for (int i = 0; i < split.length; i++)
{
sum += sdf.parse(split[i]).getTime();
}
Date avgDate = new Date((sum/split.length));
System.out.println("avg Date is:"+sdf.format(avgDate));
Convert to java.util.Date and then you can do all kinds of operations.
Check Simple Date Format and Date

Java split two integers from a string into double (converting time)

Part of an assignment I have for a beginning Java class is to take a time entered in as a string and convert it (while rounding to the nearest quarter hour) to a double and store it in an array. The part I am having difficult with is what to do with the two integers I receive from the split method of the String class. How do I make the two integers into one double to use in the array? (So it would be like hours.minutes, or 5.25)
Here is a snippet of code from a program I am working on:
public static double convertClockOutTimes(String clockOut){
double convertedTimeOut = 0;
String time = clockOut;
int hours;
int minutes;
String[]splitFields;
splitFields = time.split(":");
hours = Integer.parseInt(splitFields[0]);
minutes = Integer.parseInt(splitFields[1]);
if (minutes <= 7)
{
minutes = 0;
}
else if (minutes >= 8 || minutes <= 22)
{
minutes = 15;
}
else if (minutes >= 23 || minutes <= 37)
{
minutes = 30;
}
else if (minutes >= 31 || minutes <= 53)
{
minutes = 45;
}
else
minutes = 0;
hours = hours + 1;
convertedTimeOut = //This is where I don't know what to do!!
return convertedTimeOut;
}

I think the trick is to use a bit of math here. You could always do the following:
double convertedTimeOut = Math.round(minutes / 15.0) * 0.25 + hours;
then you don't need the if-else tree to figure out the nearest quarter hour.
There are 15 minutes in a quarter hour, and a quarter hour is 0.25 hours. Using the formula above, you are dividing the minutes into how many quarters of an hour you've got (0-4), which you then multiply by how many hours are in a quarter hour. Then add that to the hours you've got.
Math.round just does the rounding for you.

I'm guessing what's giving you the most trouble is how to deal with the minutes. Try this:
double minutesAsDecimal = 0.01 * minutes;
So if the number of minutes was 24, you would end up with 0.24. I bet you'll know where to go from there.
Just as a side note, your if and else ifs are not doing what you think they are. But since it's homework.. Just take a closer look at your logic there.

Your conditions should be AND not OR:
if(minutes >= 8 && minutes <= 22)
Etc, or better yet, a single statement, simply
minutes = ((minutes + 7) % 15) * 15;
which calculates the rounding using arithmetic rather than logic.

Convert simple time format to Special time format (hhmmt)

I'm trying to convert the time format (hh:mm:ss) to this Special Time Format (hhmmt)?
The Special Time Format (STF) is a 5 digit integer value with the format [hhmmt] where hh are the hours, mm are the minutes and t is the tenth of a minute.
For example, 04:41:05 would convert to 4411.
I'm not sure how to convert the seconds value (05) to a tenth of a minute (1).
Edit:
I've incorporated Adithya's suggestion below to convert seconds to a tenth of a minute, but I'm still stuck.
Here is my current code:
String[] timeInt = time.split(":");
String hours = timeInt[0];
String minutes = timeInt[1];
double seconds = Double.parseDouble(timeInt[2]);
int t = (int) Math.round(seconds/6);
if (t>=10) {
int min = Integer.parseInt(minutes);
// min+=1;
t = 0;
}
String stf="";
stf += hours;
stf += minutes;
stf += String.valueOf(t);
int stf2 = Integer.parseInt(stf);
return stf2;
I'm using a String to store the minutes value but it makes it difficult to increment it since it is a String and not a Integer. But when calculating the "t" (tenth of minute) I have to add 1 to minutes if it exceeds 10. If I were to use parseInt again it will exclude the 0 in front of minutes again.
How can I retain the leading zero and still increment the minutes?
Thanks.

I am guessing, its the value of seconds, compared to the tenth of a minute, which is 6 seconds. So formula for t would be
t= seconds/6 //rounded off to nearest integer
This makes sense as this value is always between 0 and 9, as seconds range from 0 and 59, so its always a single digit
For your example
t = 5/6 = 0.833 = rounded off to 1

Note the 6.0f in the division - this helps you avoid the INT truncation.
string FormatSpecialTime(string time)
{
if (time.Length != 8) throw YourException();
int HH, mm, SS, t;
if (!int.TryParse(time.Substring(0, 2), out HH)) HH = 0;
if (!int.TryParse(time.Substring(0, 2), out mm)) mm = 0;
if (!int.TryParse(time.Substring(0, 2), out SS)) SS = 0;
t = (int) Math.Round(SS / 6.0f);
if (t >= 10)
{
mm++;
t = 0;
}
if (mm >= 60)
{
HH += mm / 60;
mm = mm % 60;
}
return HH.ToString() + (mm > 10 ? mm.ToString() : #"0" + mm) + t;
}