title: Bounding generics with 'super' keyword
body: <p>Why can I use <code>super</code> only with wildcards and not with type parameters?</p>
  
  <p>For example, in the <code>Collection</code> interface, why is the <code>toArray</code> method not written like this</p>
  
  <pre><code>interface Collection&lt;T&gt;{
      &lt;S super T&gt; S[] toArray(S[] a);
  }
  </code></pre>