title: Immutable class with reference of mutable class
body: <p>Suppose I am creating a immutable class Employee which has has mutable class reference Address. how can we create the immutable class with scenario. </p>
  
  <p>I just refer to this link <a href="http://docs.oracle.com/javase/tutorial/essential/concurrency/imstrat.html" rel="nofollow" title="link">click here</a>. I did not understand this point:</p>
  
  <blockquote>
    <p>Don't share references to the mutable objects. Never store references
    to external, mutable objects passed to the constructor; if necessary,
    create copies, and store references to the copies. Similarly, create
    copies of your internal mutable objects when necessary to avoid
    returning the originals in your methods.</p>
  </blockquote>