title: Array stream not summing
body: <p>I'm trying to sum an array of Integers. I red @ZouZou 's solution from <a href="https://stackoverflow.com/questions/4550662/how-do-you-find-the-sum-of-all-the-numbers-in-an-array-in-java">this question</a> and can't get it to work</p>
  
  <pre><code>int [] arr = {1,2,3,4};
  int sum = Arrays.stream(arr).sum(); //prints 10
  </code></pre>
  
  <p>I've got</p>
  
  <pre><code>public static void proc(Integer[] v) {
      int sum = Arrays.stream(v).sum();
  </code></pre>
  
  <p>and the compiler gives "cannot find symbol method sum".</p>
  
  <p>What is the problem? Is doing it this way any faster than summing with a loop?</p>