title: Why StringBuilder when there is String?
body: <p>I just encountered <code>StringBuilder</code> for the first time and was surprised since Java already has a very powerful <code>String</code> class that allows appending.</p>
  
  <p>Why a second <code>String</code> class?</p>
  
  <p>Where can I learn more about <code>StringBuilder</code>?</p>