title: Design Pattern - sending notification to specific observer
body: <p>In my application, there are many observers and one subject, but I want to send notification to specific observers on some change in variables.</p>
  
  <p>I am getting confused and I searched about it on internet too..but haven't got much.</p>
  
  <p>I am sorry if it has been asked earlier...right now I am not able to find some concise answer.</p>