title: String.format() vs string concatenation performance
body: <p>is there any difference in performance between these two idioms ?</p>
  
  <pre><code>String firstStr = "Hello ";
  String secStr   = "world";
  String third = firstStr +  secStr;
  </code></pre>
  
  <p>and</p>
  
  <pre><code>String firstStr = "Hello ";
  String secStr   = "world";
  String third = String.format("%s%s",firstStr , secStr);
  </code></pre>
  
  <p>I know that concatenation with + operator is bad for performance specially if the operation is done a lot of times, but what about String.format() ?  is it the same or it can help to improve performance?</p>