how to convert ArrayList> to int[][]?

Question

I have an old function I can't change who want an int[][] for parameter is there a way to map ArrayList<ArrayList<Integer>> to int[][]

score 7 · Accepted Answer · edited Oct 23 '11 at 12:10

7

Get the size of the ArrayLists into i and j ,respectively Increment i and j according to your logic

int i = 0;
for(ArrayList<Integer> a1 : outer){
    int j=0;
    for(Integer k : a1){
       yourarray[i][j++] = k;
    }
    i++;
}

edited Oct 23 '11 at 12:10

Thomas Jungblut

answered Oct 23 '11 at 11:15

ashutosh raina

any reason for the down vote ? if i am wrong at-least ,provide a reason , so that i can learn. – ashutosh raina Oct 23 '11 at 11:44
1

Hi sorry, you are never resetting "j". This will yield to fancy Index Out of Bounds exceptions. And in Java you should write variable names lowercase. – Thomas Jungblut Oct 23 '11 at 11:51

score 1 · Answer 2 · edited May 23 '17 at 12:03

1

I agree with Maurice.

To convert List<Integer> to int[], there's a nice answer here that you may find usefull.

Also note that Apache Commons has a ArrayUtils class, which has a method toPrimitive() that does exactly this for one array level.

Edit (see comments below):

msandiford also mentions the existence of guava Ints class that provides a static int[] toArray(Collection<Integer> collection) method.

edited May 23 '17 at 12:03

Community

answered Oct 23 '11 at 11:15

Laurent'

Added Apache Commons ArrayUtils class for completeness – Laurent' Oct 23 '11 at 11:19
Google guava has com.google.common.primitives.Ints which has a `toArray(Collection)` method that's probably more efficient than `toPrimitive(foo.toArray())`. http://docs.guava-libraries.googlecode.com/git-history/v10.0.1/javadoc/com/google/common/primitives/Ints.html#toArray(java.util.Collection) – clstrfsck Oct 23 '11 at 11:40

score 0 · Answer 3 · answered Oct 23 '11 at 11:00

0

I guess you will need two levels of loops to do that.

answered Oct 23 '11 at 11:00

Maurice Perry

there is not default util method? – Christophe Debove Oct 23 '11 at 11:13
no: toArray cannot be used because invoking it on one of the inner lists will give an Integer[] which is different from an int[]. – Maurice Perry Oct 23 '11 at 11:20

3 Answers3