title: The difference between virtual, override, new and sealed override
body: <p>I'm pretty confused between some concepts of OOP: <code>virtual</code>, <code>override</code>, <code>new</code> and <code>sealed override</code>. Can anyone explain the differences?</p>
  
  <p>I am pretty clear that if the derived class method is to be used, one can use the <code>override</code> keyword so that the base class method will be overriden by derived class. But I'm not sure about <code>new</code>, and <code>sealed override</code>.</p>