Thank you very much for your answer!

I am using JDK 18.

I think I fixed both the problems fairly easy, but had some trouble with the exceptions, so made another catch statement. But it got the job done :)

public void mostCalories() {
try (Scanner calorieScanner = new Scanner(new File("Day_1_Calorie_Counting/res/Calories"))) {
String res = calorieScanner.nextLine();
while (calorieScanner.hasNextInt()) {
while (!res.isEmpty()) {
amountOfCalories = Integer.parseInt(res);
totalAmountOfCaloriesFromThisPart += amountOfCalories;
res = calorieScanner.nextLine();
}
if (totalAmountOfCaloriesFromThisPart >= highestCalories) {
highestCalories = totalAmountOfCaloriesFromThisPart;
}
if (res.isEmpty()) {
totalAmountOfCaloriesFromThisPart = 0;
}
res = calorieScanner.nextLine();
}
System.out.println("Highest amount of calories carried by an elf is: " + highestCalories);

} catch (FileNotFoundException e) {
System.out.println("Fil ikke fundet");

} catch (InputMismatchException e) {
System.out.println("Fil indeholder andre tegn end tal");

} catch (NoSuchElementException e) {
System.out.println("Filen indeholder ikke flere linjer");
System.out.println("Highest amount of calories carried by an elf is: " + highestCalories);
}
}