Java Collection methods
<p>I'm starting to learn Java and I have a question about generics.</p>

<p>In this methods from <code>Collection&lt;E&gt;</code> interface:  </p>

<p><code>boolean containsAll( Collection &lt;?&gt; c);<br>
boolean removeAll(Collection&lt;?&gt; c);<br>
boolean retainAll ( Collection &lt;?&gt; c);</code></p>

<p>Why is the parameter  <code>Collection &lt;?&gt; c</code> instead of <code>Collection &lt;E&gt; c</code>?</p>

<p>Thanks a lot</p>
