title: How to reach extended class' function?
body: <p>I have an Vehicle class. From Vehicle, I extend Car class (and some others like Bus, Bike..). Now in my application, I don't know  what kind of vehicle the user will want to work with. So I create a Vehicle object and later asign it the proper object (Car, Bus, ...). After that I want to call some Car's function - but I can't reach it. Why?</p>
  
  <pre><code>Vehicle vehicle=null;
  . . .
  vehicle=new Car();
  vehicle.someMethodFromCar(); //can't reach it
  </code></pre>