title: super keyword in generics
body: <pre><code>  Set&lt;? super TreeMap&gt; setOfAllSuperTypeOfTreeMap  = new HashSet&lt;SortedMap&gt;();
  
    SortedMap&lt;String,String&gt; sm = new TreeMap&lt;String,String&gt;();
    TreeMap&lt;String,String&gt; tm = new TreeMap&lt;String,String&gt;();
    setOfAllSuperTypeOfTreeMap.add(sm); //???I do not understand at all. How then could new HashSet&lt;SortedMap&gt; be ok?
    setOfAllSuperTypeOfTreeMap.add(tm); 
  </code></pre>
  
  <p>I do not understand at all. How then could new HashSet be declared at all? And what good does it do since SortedMaps can not be added anyway.</p>