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!

Answer 1

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;
}