Returning a single array to a multidimensional array

Question

Full disclosure; I needed to know this for an assignment. I wanted to return a single array to a multidimensional array from a method. I circumvented the issue with the below code by returning it to another 1-dimensional array then using a for loop to transfer values.

public class test 
{
    public static void main ( String args[] )
    {
        int[][] array1 = new int [100][5];
        int[] temp = new int [5];
        int num = 0;

        temp = setValue();

        for (int i = 0; i<=4; i++) // cycle 1
        {
            array1[num][i]= temp[i];
        }

        System.out.format("\n\n");

    }

    public static int[] setValue()
    {
        int[] array3 = new int [5];

        for (int i = 0; i<=4; i++)
        {
            array3[i]= 2;
        }

        return array3;
    }
}

Is there a more conventional way to return array3 to array1 without cycle 1? Something along the lines of

array1[num][] = setValue();

You can replace the for-loop for the second dimension ([5]) by a call to java.util.Arrays.copyOfRange but one loop for the first dimension is necessary (but not contained in your code). — Michael Butscher
– Michael Butscher, Commented Oct 12, 2018 at 0:13
One remark yet: A multidimensional Java array isn't like such an array in C/C++ (where it is just a 1-dim array with different indexing). It is a 1-dim array of references to arrays of the second dim. — Michael Butscher
– Michael Butscher, Commented Oct 12, 2018 at 0:22

Andreas · Accepted Answer · 2018-10-12 00:37:26Z

3

Comments:

The method returns a new array, so no need to initialize temp, or better yet, initialize it to return value:
```
int[] temp = setValue();
```
Java doesn't have 2D arrays, just arrays of arrays, so the entire inner array can be replaced, instead of copying values:

~~for (int i = 0; i <= 4; i++) // cycle 1~~
~~{~~
array1[num] = temp;
~~}~~
When you do that, you shouldn't allocate the inner arrays, i.e. replace [5] with []:
```
int[][] array1 = new int[100][];
```

Now there is actually no need for temp anymore, leaving main as just:

int[][] array1 = new int[100][];
int num = 0;

array1[num] = setValue();

Since you probably want to fill the entire 2D array:

int[][] array1 = new int[100][];

for (int num = 0; num < array1.length; num++) {
    array1[num] = setValue();
}

answered Oct 12, 2018 at 0:37

Andreas

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Scary Wombat · Accepted Answer · 2018-10-12 00:40:01Z

2

As @VinceEmigh hinted above you can simply do array1[num] = setValue();

see

int arr[][] = new int[5][];

for (int x = 0; x < arr.length; x++) {
    arr[x] = setValue();
}
for (int x = 0; x < arr.length; x++) {
    for (int y = 0; y < arr[x].length; y++) {
        System.out.println(arr[x][y]);
    }
}

edited Oct 12, 2018 at 0:40

answered Oct 12, 2018 at 0:37

Scary Wombat

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