title: interface/abstract class
body: <p>i have read some lines from somewhere but i cant understand the meaning of this line clearly .. i dont know why i cant understand. I know the difference between this two very well.. But plz help me .. and explain that what it does mean... ?</p>
  
  <blockquote>
    <p><strong>In design, you want the base class to present only an interface for its
    derived classes. This means, you don’t
    want anyone to actually instantiate an
    object of the base class. You only
    want to upcast to it (implicit
    upcasting, which gives you polymorphic
    behaviour), so that its interface can
    be used. This is accomplished by
    making that class abstract using the
    abstract keyword. If anyone tries to
    make an object of an abstract class,
    the compiler prevents it.</strong></p>
  </blockquote>
  
  <p>Thanks in advance....</p>