title: Difference between subclass and category?
body: <blockquote>
    <p><strong>Possible Duplicate:</strong><br>
    <a href="https://stackoverflow.com/questions/522341/difference-between-inheritance-and-categories-in-objective-c">Difference between inheritance and Categories in Objective-c</a><br>
    <a href="https://stackoverflow.com/questions/13344075/whats-the-difference-and-use-of-categories-and-inheritance">What’s the difference and use of categories and inheritance?</a>  </p>
  </blockquote>
  
  
  
  <p>thanks for your reply,for example we have nsstring class if we want to add methods to that class there is no need to create category for that,just we can subclass it but why we are using categories?Please help on this</p>