title: changing the index positioning in InputStream
body: <p>I have a binary file which contains keys and after every key there is an image associated with it. I want to jump off different keys but could not find any method which changes the index positioning in input stream. I have seen the <code>mark()</code> method but it does not jump on different places.</p>
  
  <p>Does anybody have any idea how to do that?</p>