Язык Java 7 по умолчанию

У вас есть несколько вариантов. Вы можете использовать агрегацию так

class normalClass
{
  protected $superClass;

  public function __construct( superClass $superClass )
  {
    $this->superClass = $superClass;
  }

  public function someMethod()
  {
    $this->superClass->doSomething();
  }
}

class superClass
{
  public function __construct()
  {
    $inst = new normalClass( $this );
    $inst->someMethod();
  }

  public function doSomething()
  {  //this method shall be be accessed by domeMethod form normalClass
  }
}

Или просто прямолинейный сеттер

class normalClass
{
  protected $superClass;

  public function setSuperClass( superClass $superClass )
  {
    $this->superClass = $superClass;
  }

  public function someMethod()
  {
    if ( !isset( $this->superClass ) )
    {
      throw new Exception( 'you must set a superclass' );
    }
    $this->superClass->doSomething();
  }
}

class superClass
{
  public function __construct()
  {
    $inst = new normalClass();
    $inst->setSuperClass( $this );
    $inst->someMethod();
  }

  public function doSomething()
  {  //this method shall be be accessed by domeMethod form normalClass
  }
}