title: How to use Class<? extends Something>?
body: <p><code>SolrServer.java</code> have "add()" methods. But, "server.add()"  is failed. is If I use as follows:</p>
  
  <p>in my abstract class:</p>
  
  <pre><code>public abstract void addDocs( Class&lt;?  extends SolrServer&gt; server ) throws IOException, SolrServerException;
  </code></pre>
  
  <p>in my Implementataon class:</p>
  
  <pre><code>@Override
      public void addDocs(Class&lt;? extends SolrServer&gt; server) throws IOException, SolrServerException {
          ...
          server.add(doc);        
      }
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/4BB2j.png" alt="enter image description here"></p>
  
  <p>No problem, If I use as follows:</p>
  
  <pre><code>@Override
      public void addDocs(SolrServer server) throws IOException, SolrServerException {
         ...    
         server.add(doc);        
      }
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/93CQY.png" alt="enter image description here"></p>
  
  <p>What is wrong? </p>
  
  <p><strong>UPDATE:</strong></p>
  
  <p><code>SolrServer.java</code> is an abstact class. For this reason, the problem could be?</p>