title: Why List<List<Integer>> list = new ArrayList<ArrayList<Integer>>() ;is wrong?
body: <p>why the following code is wrong in Java?</p>
  
  <pre><code>List&lt;List&lt;Integer&gt;&gt; list = new ArrayList&lt;ArrayList&lt;Integer&gt;&gt;();
  </code></pre>
  
  <p>I know <code>List&lt;List&lt;Integer&gt;&gt; list = new ArrayList&lt;List&lt;Integer&gt;&gt;()</code> is correct.</p>