Cast Object to Array

Question

So I have an Object which MIGHT be an array. It can also be primitive, or a string. If it is an array, it can be an array of literally anything.

I have no problem figuring out if it is an array but I can't seem to cast it into anything that I can iterate through to get the values out of.

// o is an object and clazz is the class of the o
if (clazz == Array.class) {
            Class ofArray = o.getClass().getComponentType();
            String arrayType = ofArray.getName(); // 'Double' for my test case
            //ERROR: [D cannot be cast to [Ljava.lang.Object 
            Object[] objects = (Object[]) o; 
    }

My background is in ruby and php (where it would just work) and the static typing is messing with my head. Any ideas?

EDIT:

This throws the error

[D cannot be cast to [Ljava.lang.Object.

What am I missing?

if (o.getClass().isArray()) {
    Object[] objects = (Object[]) o;  
}

Answer 1

If you do not want to make the switch for all primitive types you could do like this:

if (ofArray.isPrimitive()) {
    int length = Array.getLength(o);
    for (int i = 0; i < length; i++) {
        Object obj = Array.get(o, i);
        System.out.println(obj);
    }
}
else {
    Object[] objects = (Object[]) o;
    for (Object obj : objects) {
        System.out.println(obj);
    }
}

Edit: If you don't want to loop in two different places in your code use this method to convert the primitive arrays to an object array:

static Object[] convertToObjectArray(Object array) {
    Class ofArray = array.getClass().getComponentType();
    if (ofArray.isPrimitive()) {
        List ar = new ArrayList();
        int length = Array.getLength(array);
        for (int i = 0; i < length; i++) {
            ar.add(Array.get(array, i));
        }
        return ar.toArray();
    }
    else {
        return (Object[]) array;
    }
}

Answer 2

This will work for arrays with elements that are sublcasses of Object :

if (clazz.isArray()) {
    Object[] objects = (Object[]) o;
    for (Object obj : objects)
        System.out.println(obj);
}   

If you need to cast the array to an specific array type you could (ab)use instanceof but for, say, just printing the contents as strings, an Object[] suffices.

UPDATE

If the array is of primitive types, you have no option but to test for each one and cast to the correct type, Object[] won't work for this case - but there aren't that many primitive types in Java, so it won't be a gigantic switch :) . This is what I mean:

if (clazz.isArray()) {
    if (clazz.getComponentType().equals(double.class)) {
        double[] numbers = (double[]) o;
        for (double d : numbers)
            System.out.println(d);
    }
}  

Answer 3

You cannot type cast an Array of primitives to an Object[]

if (clazz == Array.class) {
  Class ofArray = o.getClass().getComponentType();
  // String arrayType = ofArray.getName(); // 'Double' for my test case
  if (ofArray instanceof double.class)
    double[] doubles = (double[]) o;
  for (double d: doubles)
    System.out.println(d);
}

To create an Object[] without instanceof checks

if (!(o instanceof Object[])) {
  int len = Array.getLength(o);
  Object[] objects = new Object[len];
  for (int i = 0; i < len; i++)
    objects[i] = Array.get (o, i);
  for (Object obj: objects)
    System.out.println(obj);
}

Answer 4

It's not enough to know your Object is an array - you should also know the underlying type of the array elements. If your array elements are of primitive type, say double , you need to

double[] doubleArray = (double[]) o;  

This won't work:

Object[] objects = (Object[]) o;