title: Collect method for streams doesn't work as expected
body: <p>I'm testing the <code>collect</code> method for streams.  In this code I'm trying to build a single string from a stream of string by using a <code>StringBuilder</code> in the first case and concatenation of <code>String</code> in the second case.  I am not understanding why the second case produces an empty string.</p>
  <pre><code>    String[] strs = new String[] {&quot;aaaaa&quot;, &quot;bbbbbbb&quot;, &quot;c&quot;, &quot;dd&quot;};
      
      
      StringBuilder sb = Arrays.stream(strs).collect(StringBuilder::new, StringBuilder::append, StringBuilder::append);
      
      System.out.println(sb);
      
      
      String s = Arrays.stream(strs).collect(String::new, String::concat, String::concat);
      
      System.out.println(s);
  </code></pre>