Java generic array deep copy and cloning generic object

Question

I would like to do a deep copy of a primitive array of n dimensions.

public static double[] deepCopy(double[] arr) {
    return arr.clone();
}

public static double[][] deepCopy(double[][] arr) {
    arr = arr.clone();
    for (int i = 0; i < arr.length; i++) {
        arr[i] = deepCopy(arr[i]);
    }
    return arr;
}

public static double[][][] deepCopy(double[][][] arr) {
    arr = arr.clone();
    for (int i = 0; i < arr.length; i++) {
        arr[i] = deepCopy(arr[i]);
    }
    return arr;
}

Above is the code to deep copy a double array of 1, 2, and 3 dimensions. I would like to generalize for any primitive type and/or generalize for the dimension of the array. I would like both, but I know a lot of things in Java are not possible, so it is okay if you can only get one, or tell me why it wouldn't work.

Thank you!

Is there any way I can do a deep copy of an n dimensional array of a primitive type? I only needed clone because I would be cloning the arrays. — akarshkumar0101, Jul 29 '18 at 21:26
@Andreas that reply was not helpful *at all*. I wanted a method to do something based on an abstract dimensional array. I already have code that can do it for 1,2,and 3 dimensional arrays, I was looking for abstraction. — akarshkumar0101, Jul 29 '18 at 22:12
You already have code? Hmmm.... I can't seem to see that anywhere in your question. --- http://idownvotedbecau.se/nocode/ — Andreas, Jul 29 '18 at 22:14

score 2 · Accepted Answer · answered Jul 29 '18 at 22:40

To deep copy a multi-dimensional array, use the following code.

Note that this is only a deep copy of array values, not of any non-array values in the array, so the copy is only truly deep for multi-dimensional primitive arrays. It is deep-shallow for multi-dimensional object arrays.

The declared type of the array doesn't matter. E.g. an Object[][] can contain array-objects, making it (partially) a 3D array. Those 3rd dimension arrays are copied too.

The method will copy 1-dimensional object arrays, but not 1-dimensional primitive arrays. To copy 1-dimensional primitive arrays, use clone().

@SuppressWarnings("unchecked")
public static <T> T[] deepCopyArray(T[] array) {
    return (T[]) deepCopyArrayInternal(array);
}
private static Object deepCopyArrayInternal(Object array) {
    int length = Array.getLength(array);
    Object copy = Array.newInstance(array.getClass().getComponentType(), length);
    for (int i = 0; i < length; i++) {
        Object value = Array.get(array, i);
        if (value != null && value.getClass().isArray())
            value = deepCopyArrayInternal(value);
        Array.set(copy, i, value);
    }
    return copy;
}

Thank you so much! This does help a lot. – akarshkumar0101 Jul 29 '18 at 22:44 — akarshkumar0101, Jul 29 '18 at 22:44

Java generic array deep copy and cloning generic object

1 Answers1