title: fail-fast iterator
body: <p>I get this definition : As name suggest fail-fast Iterators fail as soon as they realized that structure of Collection has been changed <strong>since iteration has begun</strong>.</p>
  
  <p>what it mean by <strong>since iteration has begun</strong>? is that mean after <strong>Iterator it=set.iterator()</strong> this line of code?</p>
  
  <pre><code>public static void customize(BufferedReader br) throws IOException{  
      Set&lt;String&gt; set=new HashSet&lt;String&gt;(); // Actual type parameter added  
      **Iterator it=set.iterator();**
  </code></pre>