Creating a category via component postflight

gistfile1.aw

// Get the database object
$db = JFactory::getDbo();

// JTableCategory is autoloaded in J! 3.0, so...
if (version_compare(JVERSION, '3.0', 'lt'))
{
	JTable::addIncludePath(JPATH_PLATFORM . 'joomla/database/table');
}

// Initialize a new category
$category = JTable::getInstance('Category');
$category->extension = 'com_myextension';
$category->title = 'My Category';
$category->description = 'A category for my extension';
$category->published = 1;
$category->access = 1;
$category->params = '{"target":"","image":""}';
$category->metadata = '{"page_title":"","author":"","robots":""}';
$category->language = '*';

// Set the location in the tree
$category->setLocation(1, 'last-child');

// Check to make sure our data is valid
if (!$category->check())
{
	JError::raiseNotice(500, $category->getError());
	return false;
}

// Now store the category
if (!$category->store(true))
{
	JError::raiseNotice(500, $category->getError());
	return false;
}

// Build the path for our category
$category->rebuildPath($category->id);

https://joomla.stackexchange.com/questions/5359/create-categories-subcategories-and-articles-using-php

this solution works better for latest joomla