title: Adding subclass objects to an arraylist, at the same time not allowing super class objects into the list
body: <p>Consider the following;</p>
  
  <pre><code>class Mobile
  {
  }
  class Android extends Mobile
  {
  }
  class Iphone extends Mobile
  {
  }
  </code></pre>
  
  <p>Now I have to create a list that accepts "ONLY" the child class objects and not the super class (Mobile) object.</p>