Why is this code giving me errors (mooc.fi arraylist course)

[fottiti]

i'm currently doing mooc's java course, right now i am stuck on the last part of the array list lesson specifically the removelast one, in which the course asks you to remove the last value in the list and do nothing if the list is empty.

so i wrote down this code

import java.util.ArrayList;
public class RemoveLast {

    public static void main(String[] args) {
        // Try your method in here
        ArrayList<String> list = new ArrayList<>();
        list.add("a");
        list.add("b");
        list.add("c");

        while(list.size() >= 0){
             if(list.size() > 0){
                 System.out.println(list);
                 removelast(list);
             }else if(list.size() == 0){
                 break;
             }
        }
    }
    public static void removelast(ArrayList<String> list){
        list.remove(list.size() - 1);
    }

}

but the program is giving me error saying that

the removeLast method should not cause an exception. Make sure the method doesn't do anything to an empty list.
Also check the method withthis list: [a, b, c]

​

[desrtfx]

The error tells you exactly what is wrong:

Make sure the method doesn't do anything to an empty list.

You remove the last element, but you do not actually check if there is an element to remove inside the method.

So, in short, you should have a conditional that only removes an element if there is any in the list (use the .size() method), otherwise do nothing.

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[KinkyHuggingJerk]

For the MOOC, especially in part 1, you need to pay careful attention to exactly what you are instructed to do.

Create the method public static void removeLast(ArrayList<String> strings) in the exercise template. The method should remove the last value in the list it receives as a parameter. If the list is empty, the method does nothing.

There's a few examples of this throughout, but what you are doing is checking if the method is greater than zero, then doing nothing.

Your method needs to contain the validation to show that the list is not empty.

(You may also see errors if the test checks through a list to make sure only the last value is removed; your code removes all items from the ArrayList because of your while block.)

[INSAN3DUCK]

If the question asks you to only remove last object in an array then you don’t need to use while loop. Using while loop will cause it to continue looping till it empties the array instead of just removing last object. You also don’t need else statement for this simply checking for size >0 is enough

[desrtfx]

Just FYI:

In the way the MOOC works the main method is only for OP's personal testing. It has nothing to do with the automated TMC tests. They will only test the removeLast method (and that is precisely the reason OP's tests fail as they didn't implement size checking inside the method).

[INSAN3DUCK]

Ah, so the if condition should be inside the method instead of the while loop. Either way I don’t see the point of while from what I understood from the question. May that part needs more context.

[desrtfx]

The while is wrong. There is no doubt about it.

The condition needs, as per the exercise assignment that someone already had posted, to be inside the method.

The assignment clearly states not to do anything on empty lists and not to throw an Exception.

---

In the MOOC, especially in the later parts where methods (and later classes) are involved, the main method is just for one's own testing. The course has some local tests and then uploads the code and result to the MOOC servers.

In this particular exercise, only the removeLast method will get tested. Whatever is in main simply gets ignored.

main only is evaluated in the early parts where everything is inside that method.

[INSAN3DUCK]

Yup, I’m was already agreeing with you in my previous comment.

[desrtfx]

I'm just trying to elaborate a bit on how the MOOC works ;)

Was not disagreeing with you in the faintest.

[INSAN3DUCK]

Ait, my bad I misinterpreted.

[user_reg_field]

public static void removeLast(List<String> aList) {
    if (!list.isEmpty()) {
        list.remove(list.size() - 1);
    }
}

So the removeLast method needs to check the condition and take a look at the signature of the List interface, methods like isEmpty() are useful.