Not Able to Access size or element of Nested list

Question

I'm getting error while accessing the size or element of inner list in Java.

public static void main(String... args) {
    List list = new ArrayList();

    List<Integer> list2 = Arrays.asList(1,2,3);
    List<Integer> list3 = Arrays.asList(5, 6);
    List<Integer> list4 = Arrays.asList(7, 8, 9);

    list.add(list2);
    list.add(list3);
    list.add(list4);

    for (int i = 0; i < list.size(); i++) {
        for (int j = 0; j < list.get(i).size(); j++) {
            System.out.print(list.get(i).get(j)+ " ");
          }
       }
    }
}

Does this answer your question? [What is a raw type and why shouldn't we use it?](https://stackoverflow.com/questions/2770321/what-is-a-raw-type-and-why-shouldnt-we-use-it) — Savior, Apr 07 '20 at 20:00
It's better to copy your stacktrace to your question, instead of attaching it as an image. — henriqueor, Apr 07 '20 at 20:11

score 1 · Accepted Answer · answered Apr 07 '20 at 19:39

Your declaration of the list q is missing the information of what kind of objects it contains.

List<List<Integer>> q = new ArrayList<>();

Without this information, the only thing the compiler can know is that it contains objects of some kind, so q.get() must have type Object. But there are no get() nor size() methods in Object class, and that's the error you get.

score 0 · Answer 2 · answered Apr 07 '20 at 19:39

0

You should be using List<List<Integer>> q = new ArrayList<>(); instead of List q = new ArrayList(); since you are inserting a group of lists in q.

answered Apr 07 '20 at 19:39

Majed Badawi

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score 0 · Answer 3 · answered Apr 07 '20 at 19:40

Update you loop code with following, basically you need to cast the q.get(i) into List.

 for (int i = 0; i < q.size(); i++) {
        for (int j = 0; j < ((List) q.get(i)).size(); j++) {
            System.out.print(((List) q.get(i)).get(j)+ " ");
          }
       }
    }

Hope this helps.

Not Able to Access size or element of Nested list

3 Answers3