Hi,
GenericServletClass implements ServletConfig and Servlet Interface.
the default behavior of GenericServlet class is when init() is invoked it calls init(ServletConfig) this class now has reference of ServletConfig from Servlet Container.
the extending class has to call getServletConfig() to get reference of Config from container.
getServletConfig() method call can be avoided /Extending class can obtain ServletConfig reference by calling super.init(ServletConfig).
Hope this clarifies your doubt.