How to count items of nested lists?
<p>How can I use the Stream API to count items of nested lists?</p>

<p>Imagine 3 nested lists:</p>

<pre><code>List&lt;OuterList&gt; outerLists;

class OuterList {
    List&lt;Sublist&gt; subLists;
}

class Sublist {
    List&lt;String&gt; items;
}
</code></pre>

<p>I just want to sum the number of <code>items.size()</code> of all lists. I'm trying to achive something like:</p>

<pre><code>outerLists.stream().forEach(outer -&gt; 
  outer.getSubLists().stream().forEach(sub -&gt; 
  sub.getItems().size())
 .sum/count()?
</code></pre>