converting double[][] to Double[][]

Question

I need to convert a double[][] (2D array of primitives type) into Double[][] (2D array of Double wrapper class).

Is there a better solution other than the one that I already have?

import java.util.stream.IntStream;

public class DoubleUtils {

    public static final Double[] EMPTY_DOUBLE_OBJECT_ARRAY = new Double[0];

    static final double[][] testArray = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } };

    public static Double[][] toObject(double[][] array) {
        return IntStream.range(0, array.length).mapToObj(x -> toObject(array[x])).toArray(Double[][]::new);
    }

    public static void main(String[] args) {
        Double[][] returnArray = toObject(testArray);
        System.out.println(testArray);
        System.out.println(returnArray);
    }

    /**
     * 
     * CODE FROM APACHE COMMON LANG 3
     * <p>
     * Converts an array of primitive doubles to objects.
     *
     * <p>
     * This method returns {@code null} for a {@code null} input array.
     *
     * @param array a {@code double} array
     * @return a {@code Double} array, {@code null} if null array input
     */
    public static Double[] toObject(final double[] array) {
        if (array == null) {
            return null;
        } else if (array.length == 0) {
            return EMPTY_DOUBLE_OBJECT_ARRAY;
        }
        final Double[] result = new Double[array.length];
        for (int i = 0; i < array.length; i++) {
            result[i] = Double.valueOf(array[i]);
        }
        return result;
    }

}

I know I can convert the toObject method into use lambda which would be a good approach. Any comments and/or suggestions from the community?

Thanks in advance.

Probably fine. What do you mean by "better"? There are many possible metrics. What specific problem are you having with this solution that you want to fix? — Mad Physicist, Mar 10 '20 at 15:50
I guess performance would be the most important metric. Memory usage as well would be a good to keep as low as possible. — Flavio Oliva, Mar 10 '20 at 18:27

score 1 · Accepted Answer · answered Mar 10 '20 at 16:02

You can do it also as follows:

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        double[][] testArray = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } };
        Double[][] returnArray = Arrays.stream(testArray).map(d -> Arrays.stream(d).boxed().toArray(Double[]::new))
                .toArray(Double[][]::new);
        System.out.println(Arrays.deepToString(testArray));
        System.out.println(Arrays.deepToString(returnArray));
    }
}

Output:

[[1.0, 2.0, 3.0], [4.0, 5.0, 6.0], [7.0, 8.0, 9.0]]
[[1.0, 2.0, 3.0], [4.0, 5.0, 6.0], [7.0, 8.0, 9.0]]

converting double[][] to Double[][]

1 Answers1