title: How to add an object to pair of pair list in Java?
body: <p>the list type:</p>
  
  <pre><code>List&lt;Pair&lt;Integer, Pair&lt;Integer, Integer&gt;&gt;&gt; listPairOfPair = null;
  </code></pre>
  
  <p>I tried these but it didn't work:</p>
  
  <pre><code>listPairOfPair.add(new Pair&lt;Integer, Pair&lt;Integer, Integer&gt;&gt;(1, (2,3));
  
  listPairOfPair.add(new Pair&lt;Integer, Pair&lt;Integer, Integer&gt;&gt;(1, Pair.create(2,3)));
  </code></pre>