title: How can abstract classes have references but not objects?
body: <p>Note that you cannot construct an object of an abstract class, but you can still have an object
  reference whose type is an abstract class. Of course, the actual object to which it refers must be
  an instance of a concrete subclass:</p>
  
  <pre><code>Account anAccount; // OK
  anAccount = new Account(); // Error—Account is abstract
  anAccount = new SavingsAccount(); // OK
  anAccount = null; // OK
  </code></pre>
  
  <p>Not understanding why you can have an object reference to an abstract class...</p>