how to retrive subcategory in wordpress?

 <?php
$subcategories = get_categories('&child_of=6&hide_empty');
echo '<ul>';
foreach ($subcategories as $subcategory) {
  echo sprintf('<li><a href="%s">%s</a></li>', get_category_link($subcategory->term_id), apply_filters('get_term', $subcategory->name));
}
echo '</ul>';
?>