I don't understand why it isn't creating a n - java help on CodeGym

Hello, I go to Run -> Edit configurations -> I add the program arguments -c Washington m "04 15 1990". This, normally should create a new person and add it to the list, no? At least this is what I understand from the switch case "-c". Then, I go back to Run -> Edit configurations -> I add the program arguments -i 2 . This, normally then should print the information of the 3 elements of the arraylist. In main, I print args[2]; however I get the ArrayIndexOutOfBounds error which means the arguments from the beginning were not added to the array list. What is happening?

public class Solution {
    public static List<Person> allPeople = new ArrayList<>();

    static {
        allPeople.add(Person.createMale("Donald Chump", new Date()));  // id=0
        allPeople.add(Person.createMale("Larry Gates", new Date()));  // id=1
    }

    private static SimpleDateFormat simpleDateFormat = new SimpleDateFormat("MM dd yyyy", Locale.ENGLISH);
    private static SimpleDateFormat simpleDateFormat2 = new SimpleDateFormat("MMM dd yyyy", Locale.ENGLISH);

    public static void main(String[] args) throws Exception {
        //for (int i = 0; i < args.length; i++){
            System.out.println(args[0]);
        //}

            if (args == null || args.length < 1)
            throw new RuntimeException();

        Date birthdayDate;
        Person person;
        switch (args[0]) {
            case "-c":
                birthdayDate = simpleDateFormat.parse(args[3]);

                if (args[2].equals("m"))
                    person = Person.createMale(args[1], birthdayDate);
                else
                    person = Person.createFemale(args[1], birthdayDate);

                allPeople.add(person);
                System.out.println(allPeople.size() - 1);
                break;
            case "-u":
                birthdayDate = simpleDateFormat.parse(args[4]);
                int id = Integer.parseInt(args[1]);
                person = allPeople.get(id);
                if (person == null)
                    throw new IllegalArgumentException();
                person.setSex(getSex(args[3]));
                person.setBirthDate(birthdayDate);
                person.setName(args[2]);
                allPeople.set(id, person);
                break;
            case "-d":
                Person currentPerson = allPeople.get(Integer.valueOf(args[1]));
                currentPerson.setName(null);
                currentPerson.setSex(null);
                currentPerson.setBirthDate(null);
                break;
            case "-i":
                person = allPeople.get(Integer.parseInt(args[1]));
                if (person != null)
                    System.out.println(person.getName() + " " + (person.getSex() == Sex.MALE ? "m" : "f") + " " + simpleDateFormat2.format(person.getBirthDate()));
                break;
        }
    }

    private static Sex getSex(String sexParam) {
        return sexParam.equals("m") ? Sex.MALE : Sex.FEMALE;
    }
}

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Andrei

Level 41

8 January 2021, 07:50

Wait, I think I understand. If I am correct, line 14

System.out.println(args[0]);

is useless because the relevant switch cases already have print method included. So after I add -c washington etc all I have to do is switch this argument with -i and 2 and the information will be printed by itself.

8 January 2021, 07:53

But still, I have just tested again and added the new person washington as described above and it prints out 2, correctly. But then, when I am replacing the arguments with -i 2 I still get the arrayindexetc error. What is going on?

8 January 2021, 08:23

Also, I have another question: In the case of deleting a person, see line 45, argument -d, wouldn't it be easier to just remove that person from the list of persons instead of replacing all of its values with null?

Nouser

Level 36 , Germany

8 January 2021, 09:15

-i 2 isn't showing your added user cause you haven't saved it to disk. That list entry is just added to an object memory. When you close your program (closes automatically cause it reaches the end of main) after adding a user, all objects are taken care of by the garbage collector. Means your new user went to the digital nirvana. Removing the entire line for sure is easier. That approach however makes sure the id is not getting reused.

8 January 2021, 09:30

Ah , ok, so when main ends so does the lifespan of the argument. It seems to me to be a bit strange because why would I use the argument to add the element to the list if I don't really want it added? I don't really see the logic here, maybe I am missing something. Regarding the deletion of the element. Considering that I remove the element altogether, doesn't the id automatically disappear? Let's take a hypothetical example; we have 3 elements in the allpeople array: In position 1 I have used this: -c Washington m "04 15 1990" Now, when I just delete the element doesn't element from position 2 move to position 1? What you mean is if I put null to every field, then position 1 remains in the array it just returns null, or, as configured in the program, the Runtime Exception when it is accessed? Now, why would I want to keep a null field like that?

8 January 2021, 09:48

Late you could add some way to save your list to disk. When you open the program again, it loads the user list from hd and performs its actions. As it is now it is kinda useless and just there to tell you the principles of crud. And yes, if you remove the id from the list entirely then it is gone. Elements after that user in the list will get another list index. You would need to save the id inside the Person class in that case. Otherwise you get a mess.

8 January 2021, 12:29

OK, I understand better now, thank you!

I don't understand why it isn't creating a new person to the list when passing the provided arguments in the example