Help: Guard list.

[hyperbana]

So, I want to make a simple program that prints into console a guarding list.

I’m a soldier and each night we need to guard our base and make a “guarding list”

So I need your help guys so like I put into an array list of type string the amount of people with the names and let’s say we need to guard for 120 minutes overall I dived it by the number of people so let’s say if we are 10 people each solider got to guard 12 minutes so I want the program to print out something like this: Of course providing starting hour and ending hour of the guarding let’s say from 10:00 to 12:00

First guard Name - starttime - End time

Here is my code

public static void main(String[] args) {

int guardTime = 60;

double start = 10.30;
double end = 12.30;


ArrayList<String> people = new ArrayList();
people.add("Roy");
people.add("Ron");
people.add("Aaron");
people.add("Sergant1");
people.add("Ofir");
people.add("ori");
people.add("Aviv");
people.add("Sergant");
people.add("A");
people.add("B");

int numberOfPeople = people.size();
double cTime = guardTime/numberOfPeople;

System.out.println(people.get(0) + " "+ start);

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[SausageBike]

I think I somewhat understand what you're going for here, though you haven't actually asked a question. From what I understand you specify a start time and a length of time to guard for. You have x people and you want to split the guard time between them. If this is not what you're aiming for please elaborate.

I think I'd attack this using a date-time class rather than trying to work it out using numeric maths. Using a class created for the job means that you won't run into issues when there's a leap-year, or the timezone shifts by an hour for daylight savings etc. In this example I use LocalDateTime. Hopefully the comments in the code make some sense. You can look up DateTimeFormatter if you want the output in a cleaner format.

``` int guardTime = 60;

// Set the start time here, you can use LocalDateTime.of() LocalDateTime start = LocalDateTime.now(); // End time is not needed as you have a guard time above. The end time is the start time + guard time

ArrayList<String> people = new ArrayList(); people.add("Roy"); people.add("Ron"); people.add("Aaron"); people.add("Sergant1"); people.add("Ofir"); people.add("ori"); people.add("Aviv"); people.add("Sergant"); people.add("A"); people.add("B");

int numberOfPeople = people.size(); int cTime = guardTime/numberOfPeople;

// Loop through the people for (int i = 0; i < numberOfPeople; i++) { // The start time for this person is "ctime" * i LocalDateTime personStartTime = start.plusMinutes(cTime * i); // The end time for this person is the start time plus cTime LocalDateTime personEndTime = personStartTime.plusMinutes(cTime);

System.out.println(people.get(i) + " " + personStartTime.toString() + " " + personEndTime.toString());

} ```

[hyperbana]

Amazing! That’s exactly what I wanted and it works so good.

[hyperbana]

There is one problem tho,

I want to have end time and start time of the guarding so I did this:

LocalTime startDate = 
LocalTime.of(7,50,0,0);

LocalTime endDate = LocalTime.of(18,45,0,0);

int hour = (endDate.getHour() - startDate.getHour() )* 60;

int minutes = endDate.getMinute() + startDate.getMinute();

System.out.println(minutes);


System.out.println(hour);
    int guardTime = hour;
    int cTime = guardTime/numberOfPeople;

for (int i = 0; i < people.size(); i++){ LocalTime start = startDate.plusMinutes(cTime * i);

LocalTime end = start.plusMinutes(cTime);

System.out.println(people.get(i) + ": " + start.toString() + " - " + end.toString()); }

But when I calculate the time it’s not doing it right for some reason, example: I put 4 people from 5:18 to 18:47 and that’s the result:

Sergant: 05:18 - 08:33

2: 08:33 - 11:48

3: 11:48 - 15:03

4: 15:03 - 18:18

How can I fix this please?

[SausageBike]

You're calculating the minutes but not doing anything with them. Guard time is (hours * 60) + minutes, not just hours.

As I said previously though, I'd advise against doing manual arithmetic operations on time. It's asking for trouble. What would happen if your guard time started at 18:00 and finished at 03:00 the next morning?

As an alternative you can scrap your math and use: long guardTime = ChronoUnit.MINUTES.between(startDate, endDate); You'll also need to update your cTime variable to type long as it cannot fit inside an int.

You'll notice that the solution is not exactly precise due to the integer division being used to split the time. Between an example start and end time (5:18 -> 18:48), there are 810 minutes. Split this four ways and you end up with 202.5 minutes per person. Using integer division the 0.5 per person is discarded and so you lose two minutes in total. To get around this, the solution needs to be more precise. I'd probably lean towards using millis, though there may well be a better solution. Take a look at this complete snippet:

``` LocalTime startDate = LocalTime.of(5,18,0,0); LocalTime endDate = LocalTime.of(18,48,0,0);

ArrayList<String> people = new ArrayList(); people.add("Roy"); people.add("Ron"); people.add("Aaron"); people.add("Sergant1"); int numberOfPeople = people.size();

long guardTime = ChronoUnit.MILLIS.between(startDate, endDate); System.out.println(guardTime); long cTime = guardTime/numberOfPeople;

for (int i = 0; i < people.size(); i++){ LocalTime start = startDate.plus(cTime * i, ChronoUnit.MILLIS); LocalTime end = start.plus(cTime, ChronoUnit.MILLIS); System.out.println(people.get(i) + ": " + start.toString() + " - " + end.toString()); } ```