Converting Between Subclass and Superclass Types

• Superclass references don't know the full story:

  anAccount.deposit(1000); // OK
  anAccount.addInterest();
  // No--not a method of the class to which anAccount belongs

• When you convert between a subclass object to its superclass type:
  • The value of the reference stays the same–it is the memory location of the object
  • But, less information is known about the object
• Why would anyone want to know less about an object?
  • Reuse code that knows about the superclass but not the subclass:

    public void transfer(double amount, BankAccount other)
    {
       withdraw(amount);
       other.deposit(amount);
    }

    Can be used to transfer money from any type of BankAccount