title: Main concepts in OOP
body: <p>I was once asked in an interview 'What are the 3 main concepts of OOP?'.
  I answered by saying that in my opinion there were 4 which are as follows:</p>
  
  <ul>
  <li>Inheritance</li>
  <li>Encapsulation</li>
  <li>Abstraction</li>
  <li>Polymorphism</li>
  </ul>
  
  <p>Was I correct?</p>