INHERITANCE AND POLYMORPHISM - Java Programming: From Problem Analysis to Program Design - page 677

declared in the abstract class BankAccount . Some operations common to all types of
accounts are to retrieve the account owner's name, the account number, the account
balance, make deposits, withdraw money, and create a monthly statement. So we include
methods to implement these operations. Furthermore, some of these methods will be
abstract. We also include the method toString to return the appropriate information
about the class as a string. The UML class diagram of the class BankAccount is shown
in Figure 10-8.

BankAccount (Abstract class )
#accountNumber: int
#name: String
#balance: double

+BankAccount(String, int , double )
+getAccountNumber(): int
+getBalance(): double
+getName(): String
+setName(String): void
+withdraw( double ): void
+deposit( double ): void
+createMonthlyStatement(): abstract void
+String toString()

FIGURE 10-8 UML class diagram of the class BankAccount

CheckingAccount : A checking account is a bank account. Therefore, it inherits all the
properties of a bank account. Because one of the objectives of a checking account is to be
able to write checks, we include the abstract method writeCheck to write checks. The
UML class diagram for class CheckingAccount is shown in Figure 10-9.

1
0

CheckingAccount

+CheckingAccount(String, int , double )
+writeCheck( double ): abstract void

FIGURE 10-9 UML class diagram of the class CheckingAccount

ServiceChargeChecking : A service charge checking account is a checking account.
Therefore, it inherits all the properties of a checking account. For simplicity we assume that
this type of account does not pay any interest, allows the account holder to write a limited
number of checks each month, and does not require any minimum balance. The named
constants, instance variables, and methods of this class are described in Figure 10-10, which
also shows the UML class diagram of the class ServiceChargeChecking .