Exercise: Creating Your Own Exception (Level 1)

In this exercise, you will create an OverdraftException that is thrown by the withdraw method in the Account class. In the previous design, the deposit and withdraw methods return a Boolean flag to indicate whether the operation was successful or not. This design has several flaws, one of which is that a false return value does not give the calling client any indication of why the operation was not successful. In the new design, you will use exceptions to indicate operation failure.

Figure 8-1 shows the UML class diagram of this new design. In UML parlance, the <<send>>
dependency indicates that the method on the source operation (the withdraw method) may throw an OverdraftException.

Figure 8-1 The withdraw Method Throws the OverdraftException




Preparation

Before you begin, make sure that you have changed directories to projects/BankingPrj/ using the cd command in the terminal window.

cd ~/ projects/ BankingPrj/

Task 1 - Creating the OverdraftException Class

Using a text editor, create the OverdraftException class source file in the src/com/mybank/domain/ directory. This class must satisfy the UML diagram in Figure 8-1 on page Lab 8-2.

Task 2 - Modifying the Account Class

Using a text editor, modify the Account class source file in the src/com/mybank/domain/ directory. This class must satisfy the UML diagram in Figure 8-1 on page Lab 8-2. In particular, the deposit and withdraw methods should not return a Boolean flag.

Task 3 - Modifying the CheckingAccount Class

Using a text editor, modify the CheckingAccount class source file in the src/com/mybank/domain/ directory. This class must satisfy the UML diagram in Figure 8-1 on page Lab 8-2.

Task 4 - Copying the TestBanking Class

Copy the TestBanking.java file from the resources/mod08_except/ directory into the src/com/mybank/test/ directory.

Task 5 - Compiling the TestBanking Program

On the command line, use the javac command to compile the test program.

Task 6 - Running the TestBanking Program

On the command line, use the java command to run the test program. You should see the following output:

Customer [Simms, Jane] has a checking balance of 200.0 with a 500.00 overdraft protection.
Checking Acct [Jane Simms] : withdraw 150.00
Checking Acct [Jane Simms] : deposit 22.50
Checking Acct [Jane Simms] : withdraw 147.62
Checking Acct [Jane Simms] : withdraw 470.00
Exception: Insufficient funds for overdraft protection   Deficit: 470.0
Customer [Simms, Jane] has a checking balance of 0.0

Customer [Bryant, Owen] has a savings balance of 200.0
Savings Acct [Owen Bryant] : withdraw 100.00
Savings Acct [Owen Bryant] : deposit 25.00
Savings Acct [Owen Bryant] : withdraw 175.00
Exception: Insufficient funds   Deficit: 50.0
Customer [Bryant, Owen] has a savings balance of 125.0