title: Uml class diagram for java
body: <p>i am a newbie to java.I am trying to create a library system.</p>
  
  <p>Which classes should be abstract? do i need more classes?</p>
  
  <p><a href="https://i.stack.imgur.com/3zOne.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/3zOne.png" alt="here is how far i got"></a></p>