how to convert ArrayList<ArrayList<Integer>> 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[][]

Thomas Jungblut · Accepted Answer · 2011-10-23 12:10:20Z

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, 2011 at 12:10

Thomas Jungblut

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answered Oct 23, 2011 at 11:15

ashutosh raina

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2 Comments

ashutosh raina Over a year ago

any reason for the down vote ? if i am wrong at-least ,provide a reason , so that i can learn.

Thomas Jungblut Over a year ago

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.

Community · Accepted Answer · 2017-05-23 12:03:35Z

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, 2017 at 12:03

CommunityBot

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answered Oct 23, 2011 at 11:15

Laurent'

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2 Comments

Laurent' Over a year ago

Added Apache Commons ArrayUtils class for completeness

clstrfsck Over a year ago

Google guava has com.google.common.primitives.Ints which has a toArray(Collection<Integer>) method that's probably more efficient than toPrimitive(foo.toArray()). docs.guava-libraries.googlecode.com/git-history/v10.0.1/javadoc/…

Maurice Perry · Accepted Answer · 2011-10-23 11:00:45Z

0

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

answered Oct 23, 2011 at 11:00

Maurice Perry

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2 Comments

Christophe Debove Over a year ago

there is not default util method?

Maurice Perry Over a year ago

no: toArray cannot be used because invoking it on one of the inner lists will give an Integer[] which is different from an int[].

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