使用索引在arraylist的arraylist中添加元素

Question

I have a arrayList done this way:

ArrayList<ArrayList<Double>> level = new ArrayList<ArrayList<Double>>(levels + 1);

So something like: enter image description here

What I would do is add a new element to the internal list saved in a certain index i of the external list. How can I do this?

I can't use method arrayList.add(i, 0.0); .

Answer 1

Use index from the external ArrayList and use it to add the number. Like this

level.get(i).add(1.1);

Answer 2

You need to get the list at a given position first and then insert into it the value desired.

Example:

final List<List<Double>> listOnList = new ArrayList<List<Double>>();
listOnList.add(new ArrayList<Double>());
listOnList.get(0).add(155.0);