Inheritance - Java Concepts - page 606

}
private double interestRate;
}

You may wonder why the addInterest method calls the getBalance and
deposit methods rather than directly updating the balance field of the
superclass. This is a consequence of encapsulation. The balance field was defined
as private in the BankAccount class. The addInterest method is defined in
the SavingsAccount class. It does not have the right to access a private field of
another class.

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Note how the addInterest method calls the getBalance and deposit
methods of the superclass without specifying an implicit parameter. This means that
the calls apply to the same object, that is, the implicit parameter of the
addInterest method. For example, if you call

collegeFund.addInterest();

then the following instructions are executed:

double interest = collegeFund. getBalance()
* collegeFund. interestRate / 100;
collegeFund. deposit(interest);

In other words, the statements in the addInterest method are a shorthand for the
following statements:

double interest = this. getBalance()
* this. interestRate / 100;
this. deposit(interest);

(Recall that the this variable holds a reference to the implicit parameter.)

S ELF C HECK

1. Which instance fields does an object of class SavingsAccount have?

2. Name four methods that you can apply to SavingsAccount objects.

3. If the class Manager extends the class Employee , which class is the
superclass and which is the subclass?