title: HashSet or HashMap without defining a hashCode() method in a new class
body: <ul>
  <li>What happens if you design a new class and try to insert objects of that class into a HashSet or HashMap without defining a hashCode() method? </li>
  </ul>
  
  <p>Please keep make the explanation easy. I'm studying for an exam and I'm still rusty with hashes in Java. Thank you.</p>