title: Java's Queue cannot specify limited size, so what's difference between "add" and "offer"
body: <p><strong>Java's Queue</strong>:<br>The difference between "add" and "offer" is that if the queue has been full, the "add" will cause the Exception, and "offer" just return false.<br></p>
  
  <p><strong>But my question is</strong> "when the queue can be full"?<br>
  It seems that there is no size-fixed queue in standard java, and the queue has no method to specify the size. <br><br>
  So if we continue to add/offer the element into queue, the queue will be <strong>extended automatically</strong>. </p>
  
  <ul>
  <li>If that is true, what's the difference between "add" and "offer" when
  we use it.</li>
  <li>If that is not true, how to specify the max size of a queue.</li>
  </ul>