FileType, why is the data_class property needed?

Question

symfony

Good day dear!
I'm learning Symfony3, I went through half a dozen options for creating / processing a field for uploading several files at once.
Among other things, when creating/adding a field of the FileType type , this field itself has the data_class attribute . Why the form itself has such an attribute - I understand, but why FileType has this attribute is not entirely clear to me.
VendorFile- I created this class myself, for testing
Example code:

class VendorType extends AbstractType
{
    /**
     * {@inheritdoc}
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('title')
            ->add('www')
            ->add('file1', FileType::class, [
                'multiple' => 'multiple',
                'data_class' => VendorFile::class, //вот эта строчка кода у меня вызывает непонятки
            ])
            ->add('Готово', SubmitType::class);
    }

In what case data_class, for what purposes can it be used? If not difficult, please give a simple example of how and when it can be used? If possible, I would also like to hear a little theory on this topic.
I also don't understand why the class constructor is not called VendorFile? I imagined that the properties of this class should be initialized with the properties of the UploadFile object, but apparently this is not the case.

Answer 1

->add('file1', FileType::class, [
    'multiple' => 'multiple', <-- Это булево свойство и оно не будет работать в данном случае
    'data_class' => VendorFile::class, //вот эта строчка кода у меня вызывает непонятки
])

data_class is needed to map data from $_FILES to an object.
symfony.com/doc/current/reference/forms/types/file...