title: Why And When Use ParentAbstractClass Obj =new Child Class() in C#
body: <p>Actually I don't know whether it is a stupid question but because of my curiosity I am asking my 1 question. And I have 2 questions</p>
  
  <p>1) I saw a video in YouTube about abstract class <a href="http://www.youtube.com/watch?v=yyU3bXyc_oU" rel="nofollow noreferrer">Link</a></p>
  
  <p>In that video, he is creating object of class using <code>Class Obj=new Class Obj();</code>
  And my Question is Why he didn't use <code>AbstractClass Obj=new Child Class();</code>
  Is there any difference between both? I mean between 
  Parent Obj =new Child Class(); vs. AbstractClass obj=new ChildClass(); ?</p>
  
  <p>2) My second Question is, I read a stack overflow question <a href="https://stackoverflow.com/questions/5396459/what-is-a-callback-and-how-is-it-different-from-an-update-panel-control/5396684#comment34097495_5396684">Link</a>.
  In the person who gave answer saying something about 
  View State(<code>........ and ViewState is left untouched</code>). Actually I didn't understand about viewstate in his answer. I commented for explanation but no one gave me the answer. So can any one answer me what it means?</p>
  
  <p>Some one please answer my question. And any help will be highly appreciated.</p>