How to fix ConcurrentModificationException while operating LinkedList?

Question

I was trying to make a playlist belonging to "Song" class having fields-(String) 'title' and (int) 'duration'. It doesn't have any compilation error but throws ConcurrentModificationException whenever I try to operate list.

I've tried to operate on a copy of the list but it didn't work. I've read that use of for loop throws this error but I'm only using Iterator:

while (!quit) {
        int input = s.nextInt();
        s.nextLine();
        switch (input) {
            case 0:
                System.out.println("exiting");
                quit = true;
                break;
            case 1:
                if (!goingforward) {
                    if (listIterator.hasNext())
                        listIterator.next();
                    goingforward = true;
                }
                if (listIterator.hasNext())
                    System.out.println("now playng: " + 
listIterator.next().getTitle());
                else {
                    System.out.println("At end of the list");
                    goingforward = false;
                }
                break;
            case 2:
                if (goingforward) {
                    if (listIterator.hasPrevious())
                        listIterator.previous();
                    goingforward = false;
                }
                if (listIterator.hasNext())
                    System.out.println("Now playing: " + 
listIterator.previous().getTitle());
                else {

                    System.out.println("At top of the list");
                    goingforward = true;
                }
                break;
            case 3:
                if (goingforward)
                    System.out.println("Now playing: " + 
listIterator.previous().getTitle());
                else
                    System.out.println("Now playing: " + 
listIterator.next().getTitle());
                break;
            default:
                System.out.println("invalid");

        }

Expected: Traverse through a list of songs added to the playlist with output: Now playing Why we live

1(INPUT)

Now playing Save Me

Output:

Now playing Why we live

1.Skip to forward

2.Skip to Previous

3.replay

1. quit

1(INPUT)

Exception in thread "main" java.util.ConcurrentModificationException at java.base/java.util.LinkedList$ListItr.checkForComodification(LinkedList.java:970) at java.base/java.util.LinkedList$ListItr.next(LinkedList.java:892) at Mian.main(Mian.java:49)

Answer 1

A LinkedList is not thread safe. I suggest using a data structure that is thread like Vector.

Note that using thread safe data structures will impact performance.

Other than Vector which is a legacy class you can find many data structures in the java.util.concurrent package, see what suits your needs. You can find them here.