List of List Printing in java

Question

I have the below list:

[10, 20, [44, 55], [[777, 888]]]

I wanna print like below (Index.Value):

0.10
1.20
2.0.44
2.1.55
3.0.0.777
3.0.1.888

public static void main(String a[]) {
    List<Object> list1 = new ArrayList<>();
    list1.add(10);
    list1.add(20);

    List<Object> list2 = new ArrayList<>();
    list2.add(44);
    list2.add(55);

    List<Object> list3 = new ArrayList<>();
    List<Object> list4 = new ArrayList<>();
    list4.add(777);
    list4.add(888);

    list3.add(list4);

    list1.add(list2);
    list1.add(list3);

    System.out.println(list1);
    print(list1, "");
}

static void print(List<Object> list, String s) {
    for (int i = 0; i < list.size(); i++) {
        if (list.get(i) instanceof Integer) {
            System.out.println(s + i + "." + list.get(i));
        } else {
            s = s + i + ".";
            print((List<Object>)list.get(i),s);
        }
    }
}

Above code is printing like below:

0.10
1.20
2.0.44
2.1.55
2.3.0.0.777
2.3.0.1.888

I know there is something wrong with my code. Do we have any other way to handle this? Can anyone help me out?

Answer 1

When you process the 3rd element of your outer list, you append "2." to s and assign the result to s.

Then, when you process the 4th element of your outer list, you append "3." to s and assign the result to s, so now s contains "2.3." instead of the desired "3." which should be passed to the recursive call.

You can avoid that if instead of assigning anything to s, you'd just pass s + i + "." to the recursive call.

Change

s = s + i + ".";
print((List<Object>)list.get(i),s);

to

print((List<Object>)list.get(i),s + i + ".");

Now the output will be:

0.10
1.20
2.0.44
2.1.55
3.0.0.777
3.0.1.888

The full corrected method:

static void print(List<Object> list, String s) {
    for (int i = 0; i < list.size(); i++) {
        if (list.get(i) instanceof Integer) {
            System.out.println(s + i + "." + list.get(i));
        } else {
            print((List<Object>)list.get(i),s + i + ".");
        }
    }
}