As I know, we can make create a Queue using syntax along the lines of Queue<Integer> = new LinkedList<>().
But when I try to add the ArrayList<Integer> element into the Queue<Integer> with the .add() method, it doesn't work.
I was considering two solutions to fix this issue:
Queue<ArrayList<Integer>> instead of Queue<Integer>Queue<Integer> and add the ArrayList by Queue.addAll()Which of these should I use?
Your two implementations do very different things.
Option 1 is for when you want to create a Queue of ArrayLists. In this case, each item in the queue would be a complete list, and adding a new item with .add would append one whole list to the queue. A Queue<ArrayList<Integer>> would give you a 2D structure like this:
[[1, 2, 3], [4, 5, 6], [7, 8, 9]]
Option 2 is for when you want to create a Queue of Integers. In this case, each item in the queue would be an individual number, and "adding" a list with .addAll would append each item in the list to the queue sequentially. This method would give you a 1D structure like this:
[1, 2, 3, 4, 5, 6, 7, 8, 9]
Which one is "better" depends on your use case - it's beyond the scope of this site to give you a specific recommendation given the limited information you've provided.