Symfony2 - How to use __construct() in a Controller and access Securty.Context?

I am having some trouble with Symfony2. Namely in how to use the __construct() function. the Official Documentation is shockingly bad!

I want to be able to use the following:

public function __construct()
{
    parent::__construct();
    $user = $this->get('security.context')->getToken()->getUser();
}

How ever I get the following error:

Fatal error: Cannot call constructor in /Sites/src/DEMO/DemoBundle/Controller/Frontend/HomeController.php on line 11

Line 11 is "parent::__construct();"

I removed it and got the following, new error

Fatal error: Call to a member function get() on a non-object in /Sites/vendor/symfony/symfony/src/Symfony/Bundle/FrameworkBundle/Controller/Controller.php on line 242

I think I might need to set up the ContainerInterface DIC, but I have no idea how to do this (I tried and failed, miserably)

Any ideas folks?

Update - Tried changing to extend ContainerAware and got this error:

Fatal error: Class DEMO\DemoBundle\Controller\Frontend\HomeController cannot extend from interface Symfony\Component\DependencyInjection\ContainerAwareInterface in /Sites/src/DEMO/DemoBundle/Controller/Frontend/HomeController.php on line 43

Using the following code in the controller:

<?php

namespace DEMO\DemoBundle\Controller\Frontend;

use Symfony\Component\DependencyInjection\ContainerAware;

class HomeController extends ContainerAwareInterface
{
     protected $container;

     public function setContainer(ContainerInterface $container = null)
     {
         $this->container = $container;
     }