Splitting strings in Java
I'm not sure how you got the original list-within-a-list input, but have you looked into Java Streams? Here's a tutorial that may help.

It looks like you're taking in a LinkedList, turning it into a string to manually delete the [[ and ]], splitting on comma, then adding each item to a new list.

Why not do something like the following:

private static List&lt;String&gt; splitListOfString(LinkedList&lt;String&gt; list) { 
    List&lt;String&gt; myList = new LinkedList&lt;&gt;();
    list.stream().forEach(item -&gt; myList.add(item));
    return myList;
}


In the above code, you're leaving the elements in the list (instead of converting to string), retrieving each item, then adding to your output list. It may need to be modified slightly to match your input.