String to localdatetime doesnt retunr seconds "00"

I have a method that I take a startTime String and a endTime String convert to LocalDateTime and compare the hours difference between and generate the values in a ArrayList. For example if I have startTime: "2023-09-14T12:00:00", endTime: "2023-09-14T14:00:00", the method will find the value 2023-09-14T13:00:00 and it will add it in the ArrayList. The problem is that when the values are converted from String to LocalDateTime the seconds doesnt appear in the format like this : 2023-09-14T13:00 .

 public static ArrayList<LocalDateTime> calculateHours(String startTime, tring endTime) {
        

        // Parse the combined strings to LocalDateTime
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss");
        LocalDateTime startDateTime = LocalDateTime.parse(startTime,formatter);
        LocalDateTime endDateTime = LocalDateTime.parse(endTime,formatter);

        // Calculate the difference in hours
        long hoursDifference = java.time.Duration.between(startDateTime, endDateTime).toHours();

        // Create an ArrayList to store LocalDateTime objects
        ArrayList<LocalDateTime> hoursList = new ArrayList<>();

        // Add each hour to the ArrayList with seconds included
        for (long i = 0; i < hoursDifference; i++) {
            LocalDateTime currentHour = startDateTime.plusHours(i);
            hoursList.add(currentHour);
        }
        return hoursList;
    }

Solution

The problem is that when the values are converted from String to LocalDateTime the seconds doesnt appear in the format like this : 2023-09-14T13:00 ."

That's talking about a conversion back to string, which would use LocalDateTime.toString() by default - and that omits the seconds when the value is 0, as documented. In other words, you can see the same behavior with

LocalDateTime ldt = LocalDateTime.of(2023, 9, 14, 13, 0, 0);
System.out.println(ldt); // Prints 2023-09-14T13:00

In other words, nothing is going wrong - you're just misinterpreting however you're looking at the values in the list. If you need the values to be formatted in a specific way, you'll need to specify a DateTimeFormatter (such as the one you've already created) and call ldt.format(formatter).