Inheritance - Java Concepts - page 604

Let's see how savings account objects are different from BankAccount objects. We
will set an interest rate in the constructor, and we need a method to apply that interest
periodically. That is, in addition to the three methods that can be applied to every
account, there is an additional method addInterest . The new method and instance
field must be defined in the subclass.

When defining a subclass, you specify added instance fields, added methods, and
changed or overridden methods.

public class SavingsAccount extends BankAccount
{
public SavingsAccount(double rate)
{
Constructor implementation
}
public void addInterest()
{
Method implementation
}
private double interestRate;
}

Figure 2 shows the layout of a SavingsAccount object. It inherits the balance
instance field from the BankAccount superclass, and it gains one additional
instance field: interestRate .

Next, you need to implement the new addInterest method. The method computes
the interest due on the current balance and deposits that interest to the account.

Figure 2

Layout of a Subclass Object

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