How do I add an array into an arraylist (so that it becomes a 2D arraylist) in java?

Question

I have an array:

String[] a = {"abc","def","ghi"}

Now I want to store this array into my string arraylist

ArrayList<String> arr = new ArrayList<>();

so that it becomes like this:

[["abc","def","ghi"]]

I have tried this code but it doesn't work:

arr.add(Arrays.asList(a));

Please help me

see this question https://stackoverflow.com/questions/80476/how-can-i-concatenate-two-arrays-in-java — rost, Mar 20 '22 at 05:59
In what sense does what you're doing "not work". What exactly are you expecting, and what happens? — tgdavies, Mar 20 '22 at 06:04

score 0 · Accepted Answer · answered Mar 20 '22 at 06:36

Since Arrays.asList(a) returns List, to add it to your list you need to use addAll()

arr.addAll(Arrays.asList(a));

Instead of

arr.add(Arrays.asList(a));

But the result will be ["abc","def","ghi"]

If you want to achieve this [["abc","def","ghi"]] then define your ArrayList as

List<List<String>> arr = new ArrayList<>();

score 0 · Answer 2 · answered Mar 20 '22 at 12:53

using arralist addAll() method we can do but, Using arrayList is depricated approach , use Streams instead of it:

System.out.println(Collections.singletonList(Stream.of(new String[] {"abc","def","ghi"}).collect(Collectors.toList())));

will result in:

[[abc, def, ghi]]

2 Answers2