Convert unknown type generic list to array

Question

I'm doing a mapping using reflection.

With reflection I can know if each of the the Fields of a Class refers to an attribute of type "array", and also I can get the Class with the type of the array.

Now, I want to set the value of the field of an object. Now, for some reason, I can get the data to fill the object field, but it's not in the form of an array. Is, instead, a Collection<?>.

Just to make it easy to visualize, I have some code like that:

/** create a new T instance, with the data taken from something*/
<T> T convert(Class<T> cls, Object something) {
    T obj = cls.newInstance();
    for (Field field : cls.getFields()) {
        if (field.getType().isArray()) {
            Class<?> arrayType = field.getType().getComponentType();
            Collection<?> collection = this.getData(arrayType, something);

            Object array = CONVERT(collection);

            field.set(obj, arrayData);
        }
    }
}

At the end of the day, I need to convert a Collection<?> object to (hypotetically) a ?[] object, where "?" is dinamically correct.

I know there is collData.toArray(), but it builds an Object[], witch is incompatible; and I know there is collData.toArray(T[]), but I have no idea of how to use it in this context.

Tagir Valeev · Accepted Answer · 2015-07-06 12:49:18Z

2

As you already have a component type, use Array.newInstance:

Object[] array = collection.toArray(
                    (Object[])Array.newInstance(arrayType, collection.size()));
field.set(obj, array);

edited Jul 6, 2015 at 12:49

answered Jul 6, 2015 at 12:44

Tagir Valeev

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2 Comments

Joop Eggen Over a year ago

Object array = collection.toArray(Array.newInst...); as the type is not an Object array.

Tagir Valeev Over a year ago

@JoopEggen, whatever. Any non-primitive array can be upcasted to Object[]. For this code it does not matter.

Anton Krosnev · Accepted Answer · 2015-07-06 13:07:19Z

1

Or do it the following way, which is easier to understand. Create an array and provide it as parameter to colleation.toArray :

Object[] array = collection.toArray(new Object[collection.size()] );
field.set(obj, array);

edited Jul 6, 2015 at 13:07

answered Jul 6, 2015 at 12:57

Anton Krosnev

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Comments

VLEFF · Accepted Answer · 2015-07-06 13:00:37Z

0

Collection as a toArray() function that return an array of what the Collection is filled. From the java doc :

String[] y = x.toArray(new String[0]);

answered Jul 6, 2015 at 13:00

VLEFF

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1 Comment

VLEFF Over a year ago

Yes, and if you're not a fool, you can change it as you want... Object[] y = x.toArray(new Object[0]);

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