title: Map to a running sum in Java 8
body: <p>If I have a collection:</p>
  
  <pre><code>List&lt;Long&gt; numbers = asList(2, 2, 4, 5);
  </code></pre>
  
  <p>How can I map/process these to build up a running total. To produce something like:</p>
  
  <pre><code>List&lt;Long&gt; runningTotals = asList(2, 4, 8, 13);
  </code></pre>
  
  <p>Even better, how can I build a list of something (like a tuple) so I can preserve the orignals:</p>
  
  <pre><code>((2 -&gt; 2), (2 -&gt; 4), (4 -&gt; 8), (5 -&gt; 13));
  </code></pre>