How to get Categories of custom extension or third party component

Question

I have a thirdparty component which stores its categories in #__categories table.

-----+----------------+-----------------------+-----------------------+-----
...  | extension      | title                 | alias                 | ...
-----+----------------+-----------------------+-----------------------+-----
...  | com_content    | Uncategorised         | uncategorised         | ...
-----+----------------+-----------------------+-----------------------+-----
...  | com_banners    | Sample Data-Banners   | sample-data-banners   | ...
-----+----------------+-----------------------+-----------------------+-----
...  | com_newsfeeds  | Sample Data-Newsfeeds | sample-data-newsfeeds | ...
-----+----------------+-----------------------+-----------------------+-----
...  | com_contact    | Sample Data-Contact   | sample-data-contact   | ...
-----+----------------+-----------------------+-----------------------+-----
...  | com_content    | Joomla!               | joomla                | ...
-----+----------------+-----------------------+-----------------------+-----
...  | com_thirdparty | ThirdParty Category   | thridparty-category   | ...
-----+----------------+-----------------------+-----------------------+-----
...  | ...            | ...                   | ...                   | ...
-----+----------------+-----------------------+-----------------------+-----

I can print categories from com_banners or from other core components as below,

$categories = JCategories::getInstance('Banners');
$subCategories = $categories->get()->getChildren(true);
print_r($subCategories);

But it shows

"Fatal error: Class 'ThirdPartyCategories' not found in ...\libraries\legacy\categories\categories.php on line 152"

when trying to print the categories of another extension as below,

$categories = JCategories::getInstance('ThirdParty');
$subCategories = $categories->get()->getChildren(true);
print_r($subCategories);

What do I have to do with the legacy categories in joomla libraries ?

Note: The name ThirdParty is just a placeholder, could be any third party extension's name.

Answer 1

After doing some research, it turns out that the third party component I am using doesn't have a file created as ..\components\com_thirdparty\helpers\category.php which is required to implement a class ThirdPartyCategories which extends JCategories in the component's helpers directory as described below

defined('_JEXEC') or die;

/**
 * ThirdParty Component Category Tree
 */
class ThirdPartyCategories extends JCategories
{
    /**
     * Constructor
     *
     * @param   array  $options  Array of options
     */
    public function __construct($options = array())
    {
        $options['table']      = '#__thirdparty';
        $options['extension']  = 'com_thirdparty';
        $options['statefield'] = 'published';
        parent::__construct($options);
    }
}