Basic java linked list calculator

This is my semester project where i am tasked to create a calculator that takes two liked lists and either add or subtract them.

the thing is my brain went blank at the addition and subtraction process, so far i made the program takes two separate String values that i parse-ed them into an integer through a loop and stick them in a list numberlist2.add(Integer.parseInt(String.valueOf(nums.charAt(i))));

and then i ran two loops that will make the lists even so it the first were like:

1>2>3>4>5 and the second was 7>8, it will make the second look like 0>0>0>7>8

i didn't do any of the internet solutions (which i only found two at w3schools) because they used node class which i don't remember that we had cover this topic; in case that there is no way to do it unless i use node class the good luck for me to go for an online course to learn it 😀

here is a picture of what i am tasked to end up with task , don't mind the "Do you want to continue"

here is what i came up with

System.out.print("Enter the operation process (+ or -) : ");
    process = input.nextLine().charAt(0);
    switch (process)
    {
        case '+' :
            for (int i=numberlist1.size(); i == 0 ; i-- )
            {
                sumlist.addFirst(numberlist1.get(i) + numberlist2.get(i));
            }
            break;
        case '-':
            for (int i=numberlist1.size(); i == 0 ; i-- )
            {
                sumlist.addFirst(numberlist1.get(i) - numberlist2.get(i));
            }
            break;
        default:
            System.out.println("you have not enter a proper operation process");
            break;

    }

side note: these are my vars in case you got confused and i am not sure if i need a "sumlist"

    // Declairing the lists and input method
    LinkedList<Integer> numberlist1 = new LinkedList<Integer>();
    LinkedList<Integer> numberlist2 = new LinkedList<Integer>();
    LinkedList<Integer> sumlist = new LinkedList<Integer>();
    Scanner input = new Scanner(System.in);
    String nums;
    char process;