title: What is the time complexity of adding an element at the beginning of an ArrayList?
body: <p>Say I have a ArrayList with n element in this array, and I add an element at the beginning:</p>
  
  <pre><code>myArrayList.add(0,'some value');
  </code></pre>
  
  <p>What will be the time complexity of this operation?</p>
  
  <p>The <a href="http://docs.oracle.com/javase/6/docs/api/java/util/ArrayList.html">Java Doc</a> doesn't specify this.</p>
  
  <p>Also</p>
  
  <p>I just start learning Java, and I saw the sentence</p>
  
  <pre><code>An ArrayList in Java is a List that is backed by an array.
  </code></pre>
  
  <p>What does 'backed' here mean? Thank you!</p>