How to convert List of int array to 2D Array?

Question

Given a list of int[] [{7, 0}, {7, 1}, {6, 1}, {5, 0}, {5, 2}, {4, 4}] I need to convert it into 2D Array {{7, 0}, {7, 1}, {6, 1}, {5, 0}, {5, 2}, {4, 4}} using Java 8.

Before Java 8 we could use the following logic: temp is List<int[]> which contains above list of elements. First res[][] is created of the same size as a List of elements in temp.

int[][] res = new int[temp.size()][2];
for (int i = 0; i < temp.size(); i++) {
   res[i][0] = temp.get(i)[0];
   res[i][1] = temp.get(i)[1];
}

This worked with java 8+. I don't think your problem has anything to do with the java version you are using or don't understand what is the problem at all. — user13149581
– user13149581, Commented Jul 6, 2020 at 2:50

Basil Bourque · Accepted Answer · 2020-07-06 02:33:41Z

2

Try this.

List<int[]> list = List.of(
    new int[] {7, 0}, new int[] {7, 1},
    new int[] {6, 1}, new int[] {5, 0},
    new int[] {5, 2}, new int[] {4, 4});
int[][] res = list.stream().toArray(int[][]::new);
System.out.println(Arrays.deepToString(res));

result

[[7, 0], [7, 1], [6, 1], [5, 0], [5, 2], [4, 4]]

See this code run live at IdeOne.com.

edited Jul 6, 2020 at 2:33

Basil Bourque

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answered Jul 6, 2020 at 2:29

user4910279

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3 Comments

Andreas Over a year ago

Up-voted, but list.toArray(int[][]::new) (without the stream() call) works quiet as well too, but is Java 11+. For all Java versions, not just Java 8+, list.toArray(new int[0][]) works great.

user13149581 Over a year ago

List.of is also java 9+, I don't know if using streams is any better in this case and if it solves the OP problem, if there was any.

Holger Over a year ago

Mind that this makes a shallow copy. The example code in the question does a deep copy.

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