Converting List> to Array>

Question

I am writing a method which converts Integer data type from a List of lists, to a primitive type \"int\" of \"array of array\".

Question

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Answer 1

To answer your exact question, yes an Integer can be converted to an int using the intValue() method, or you can use auto-boxing to convert to an int.

So the innermost part of your loop could be either of these:

tempArray[i][j] = ll.get(i).get(j).intValue();
tempArray[i][j] = ll.get(i).get(j);

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However, we can also take a different strategy.

As a modification of this answer to a similar question, in Java 8 you can use Streams to map to an integer array. This structure just requires an extra layer of mapping.

List> list = new ArrayList<>();

int[][] arr = list.stream()
    .map(l -> l.stream().mapToInt(Integer::intValue).toArray())
    .toArray(int[][]::new);

Ideone Demo