title: Generics wildcard confusion
body: <p>What is the functional difference between</p>
  
  <pre><code>Container&lt;Class&gt;
  </code></pre>
  
  <p>and </p>
  
  <pre><code>Container&lt;? extends Class&gt;
  </code></pre>
  
  <p>?</p>
  
  <p>Anything that inherits from <code>Class</code> is a <code>Class</code> so I don't understand why bother with <code>?</code>.</p>