if(!defined('DS')){

define('DS',DIRECTORY_SEPARATOR);

}

Controller class change from JController to JControllerLegacy

//$controller = JController::getInstance('HelloWorld');

$controller = JControllerLegacy::getInstance('HelloWorld');

 

Model class change from JModel to JModelLegacy

class HelloWorldModelHelloWorld extends JModelItemLegacy

 

View Class Change from JView to JViewLegacy

//class HelloWorldViewHelloWorlds extends JView class

HelloWorldViewHelloWorlds extends JViewLegacy

class HelloWorldController extends JControllerLegacy

 

class HelloWorldModelUpdHelloWorld extends JModelFormLegacy

JRegistry::getValue() now is JRegistry::get()

//Convert sample to JRegistry with LoadJSON - Sample from Joomla 3.0 sourcecode

// $params = new JRegistry;

// $params->loadJSON($this->item->params);

// $this->item->params = $params;

$params = new JRegistry;

$params->loadString($item->params);

$item->params = $params;

 

Database function changes -

nameQuote(joomla 2.5) - quoteName(joomla 3.0)

 

link: https://ramnihor.wordpress.com/2012/10/03/migrate-joomla-extension-from-2-5-to-3-0/