HashSet question 
<blockquote>
  <p><strong>Possible Duplicate:</strong><br>
  <a href="http://stackoverflow.com/questions/2235546/why-does-hashset-implementation-in-sun-java-use-hashmap-as-its-backing">Why does HashSet implementation in Sun Java use HashMap as its backing?</a>  </p>
</blockquote>



<p>I know what a hashset and hashmap is - pretty well versed with them.
There is 1 thing which really puzzled me.</p>

<p>Example:</p>

<pre><code>Set &lt;String&gt; testing= new HashSet &lt;String&gt;();
</code></pre>

<p>Now if you debug it using eclipse right after the above statements, under debugger variables tab, you will noticed that the set 'testing' internally is implemented as a hashmap.</p>

<p>Why does it need a hashmap since there is no key,value pair involved in sets collection</p>
