Clone a limited multi-dimensional

Question

I have this:

String[][] numbers = {
     {"one", "two", "three"},
     {"four", "five", "six"},
     {"seven", "eight", "nine"}
}

String[][] tmp;

What i what now is that i clone numbers into tmp but LIMITED to 2 arguments per row. I don't wanna initialize any size

Output of tmp:

{      
    {"one", "two"},         
    {"four", "five"},         
    {"seven", "eight"}
}

What i tried:

String[][] cloneArray(String[][] elements) {
    int length = elements.length;
    String[][] target = new String[length][2];
    for (int i = 0; i < length; i++) {
        System.arraycopy(elements[i], 0, target[i], 0, elements[i].length);
    }

    return target;
}

I can't give a particular size becouse i have a function that updates(adds) the array:

String[][] append(String[][] arr, String[] element) {
    final int N = arr.length;
    arr = Arrays.copyOf(arr, N + 1);
    arr[N] = element;
    return arr;
}

I get java.lang.ArrayIndexOutOfBoundsException

"I don't wanna initialize any size" - why not? You'd have to define the size of the target array anyway (i.e. limit it to `2` elements). — Thomas, Aug 23 '19 at 12:16
What is your question? In particular: what is wrong with your current solution? — Turing85, Aug 23 '19 at 12:20
becouse i have another function that add elements every time a button is pressed...so i need an unlimited array...i will edit the post — RaylessTiKi, Aug 23 '19 at 12:22

Fullstack Guy · Answer 1 · 2019-08-23T12:46:18.240

We can filter out the inner array beyond the second element, by getting a Stream<String[]> out of it and applying the Stream#map on it so that the size of the new inner array is limited to 2 elements:

String[][] numbers = {
                       {"one", "two", "three"},
                       {"four", "five", "six"},
                       {"seven", "eight", "nine"}
                     };
String[][] tmp = Arrays.stream(numbers)
                        .map(arr -> (arr != null && arr.length > 2)
                                         ? Arrays.copyOf(arr, 2) 
                                         : arr)
                       .toArray(String[][]::new);
System.out.println(Arrays.deepToString(tmp));

Output:

 [[one, two], [four, five], [seven, eight]]

@RaylessTiKi Glad it worked, please accept my answer if you like. — Fullstack Guy, Aug 23 '19 at 12:38

UkFLSUI · Answer 2 · 2019-08-23T14:00:52.420

You are using wrong syntax for System.arraycopy(). The declaration of the method is like this:

public static void arraycopy(Object src, int srcPos, Object dest, int destPos, int length)

Where, src and dest are source array and destination array respectively. The arraycopy function itself handles the position from srcPos to srcPos + length and copy it from destPos to destPos + length. So, no need to loop through the elements and use arraycopy() for each of them.

So, for your code, the fix will be:

String[][] cloneArray(String[][] elements) {
    int length = elements.length;
    String[][] target = new String[length][2];
    System.arraycopy(elements, 0, target, 0, elements.length);
    return target;
}

And if you don't want to use arraycopy rather want to loop through the elements and manually copy elements, you can also do that simply:

String[][] cloneArray(String[][] elements) {
    int length = elements.length;
    String[][] target = new String[length][2];
    for (int i = 0; i < length; i++) {
        for (int j = 0; j < 2; j++) {
            target[i][j] = elements[i][j];
        }
    }
    return target;
}

with your solution i don't get java.lang.ArrayIndexOutOfBoundsException anymore, but it's not working...i get a very strange output — RaylessTiKi, Aug 23 '19 at 12:30
@RaylessTiKi Please check out my latest edit, this should work. — UkFLSUI, Aug 23 '19 at 12:44

Clone a limited multi-dimensional

2 Answers2