Basically I have the following function where I need to convert ArrayList to List
public List<List<Integer>> somefunc(int[] nums) {
ArrayList<ArrayList<Integer>> a = new ArrayList<ArrayList<Integer>>();
// logic
return a;
}
How can I convert this ArrayList<ArrayList> to List<List>?
You should always prefer programming to interfaces.
Change
ArrayList<ArrayList<Integer>> a = new ArrayList<ArrayList<Integer>>();
to
List<List<Integer>> a = new ArrayList<>();
Then you can add ArrayList<Integer> instances to a.
Instead of this:
ArrayList<ArrayList<Integer>> a = new ArrayList<ArrayList<Integer>>();
Write this:
List<List<Integer>> a = new ArrayList<List<Integer>>();
Or even this:
List<List<Integer>> a = new ArrayList<>();
There is no need to "convert" it.
Just declare your a as
List<List<Integer>> a = new ArrayList<List<Integer>>();
You can add any List<Integer> to your a:
a.add(new ArrayList<Integer>());
