Java 2D arraylists ndexOutOfBoundsException: Index: 0, Size: 0

Question

I am new to Java. Trying to create 2D arraylist, but getting this indexOutOfBoundsException: Index: 0, Size: 0

ArrayList<ArrayList<Integer>> twoDArrayList = new ArrayList<>();
for (int i = 0; i < 4; i++)
{
    twoDArrayList.add(new ArrayList<>());
    twoDArrayList.get(i).set(0,1); 
}

Why second line fails in the for loop? When i = 0, there is already a row created with add(new ArrayList<>())

------------------------------- thank you for your hints! ---------------------

Now finally I have a solution to print Pascal triangle..... first 5 lines of it

ArrayList> twoDArrayList = new ArrayList<>();

    for (int i=0; i < 5; i++)
    {

        ArrayList<Integer> row = new ArrayList<>();

        for (int j = 0; j <= i ; j++)
        {
            row.add(0);
        }

        row.set(0, 1);
        row.set(i, 1);

        twoDArrayList.add(row);


        for (int j=1; j < i; j++)
        {
            twoDArrayList.get(i).set(j, twoDArrayList.get(i-1).get(j-1) + twoDArrayList.get(i-1).get(j));
        }

    }


    for (ArrayList<Integer> row: twoDArrayList)
    {
        for (Integer element: row)
        {
            System.out.printf("%4d",element);
        }
        System.out.println();
    }

What are tabs doing in your code? (Especially between operands and operators...) — Jashaszun, Jul 29 '15 at 21:45

score 1 · Answer 1 · answered Jul 29 '15 at 21:54

1

You row is created with a empty list.

The value from twoDArray.get(i) will be a list with size 0.

answered Jul 29 '15 at 21:54

Marcos Vasconcelos

18,136
30
106
167

score 0 · Answer 2 · answered Jul 29 '15 at 22:27

The arraylist set method does not add objects, but replaces with an object at a specified position.

In your first line of the for loop, you instantiate an empty arraylist. Then in your second line of the for loop, you access the newly instantiated array list and attempt to replace the element in the first position with the integer "1" - which yields a index out of bounds exception, since the first position has no element/null.

score 0 · Answer 3 · answered Jul 29 '15 at 22:33

0

ArrayList<ArrayList<Integer>> twoDArrayList = new ArrayList<>();
   for (int i = 0; i < 4; i++)
    {
       ArrayList<Integer> al = new ArrayList<>();
       al.add(i,1);
       twoDArrayList.add(al);
       twoDArrayList.get(i).set(0,1); 
    }

answered Jul 29 '15 at 22:33

Deepak Goyal

4,747
2
21
46

score -2 · Answer 4 · edited Jul 29 '15 at 22:10

-2

public <T> List<T> twoDArrayToList(T[][] twoDArray) {
    List<T> list = new ArrayList<T>();
    for (T[] array : twoDArray) {
        list.addAll(Arrays.asList(array));
    }
    return list;
}

edited Jul 29 '15 at 22:10

andrewsi

10,807
132
35
51

answered Jul 29 '15 at 21:52

ABDULNASER

1
1

1

Could you add a little explanation to your code to say what it's doing, and why? – andrewsi Jul 29 '15 at 22:10
1

please explan your answer. – Zakaria Acharki Jul 29 '15 at 22:16

Java 2D arraylists ndexOutOfBoundsException: Index: 0, Size: 0

4 Answers4