As a prerequisite

ArrayLista = new ArrayList<>();
Defined in it

1 2
3 4
5 6
7 8

Contains a value such as

. I want this to be an array,
String b = a.get (0);
String [] c = b.split ("");
System.out.println (c [0]);
And now we know that each one can be divided.

Next

Line by line
[1,2]
[3,4]
[5,6]
[7,8]

I want an array like the above,

String [] d;
for (int k = 0;k d [k] = a.add (k) .split ("");
}

I said
error: incompatible types: int cannot be converted to String
I got an error saying that, and I checked it, but I didn't understand it because there was little information.

As a clause that comes to mind, I think that list a should be a two-dimensional array.
I do not know in detail.

list a

[1,2]
[3,4]
[5,6]
[7,8]

I'd like advice on how to make it look like the above.