AP Computer Science Exam Question - Throwing Exceptions

Question:

You have been given a code snippet that models a bank account in Java. The BankAccount class has a constructor that takes an initial balance as a parameter, and two methods: withdraw and deposit for making withdrawals and deposits, respectively. The withdraw method should throw a BankAccountException if the withdrawal amount is greater than the current balance.

Your task is to complete the withdraw method and implement a BankAccountException class that extends the Exception class.

public class BankAccount {
    private double balance;

    // Constructor
    public BankAccount(double initialBalance) {
        balance = initialBalance;
    }

    // Method for withdrawing money
    public void withdraw(double amount) {
        // TODO: Add exception handling code here
    }

    // Method for depositing money
    public void deposit(double amount) {
        balance += amount;
    }
}

Instructions:

1. Implement the BankAccountException class that extends the Exception class. This exception should have a constructor that takes a message as a parameter, and passes the message to the parent Exception class.

2. Modify the withdraw method in the BankAccount class to throw a BankAccountException if the withdrawal amount is greater than the current balance.

3. If an exception is thrown, print the message "Withdrawal amount exceeds available balance" to the console.

Write the complete code for the BankAccountException class and modify the withdraw method in the BankAccount class according to the instructions.

Note: You do not have to implement any input/output logic or a main method. Just write the required classes and methods.

Answer:

public class BankAccountException extends Exception {
    public BankAccountException(String message) {
        super(message);
    }
}

public class BankAccount {
    private double balance;

    // Constructor
    public BankAccount(double initialBalance) {
        balance = initialBalance;
    }

    // Method for withdrawing money
    public void withdraw(double amount) throws BankAccountException {
        if (amount > balance) {
            throw new BankAccountException("Withdrawal amount exceeds available balance");
        }
        balance -= amount;
    }

    // Method for depositing money
    public void deposit(double amount) {
        balance += amount;
    }
}

Explanation:

1. To implement the BankAccountException class, we extend the Exception class using the extends keyword. The exception has a constructor that takes a String parameter message, and passes the message to the parent Exception class using the super keyword.

2. In the withdraw method of the BankAccount class, we add the throws BankAccountException declaration, indicating that this method can throw a BankAccountException.

3. We check if the amount is greater than the balance inside the withdraw method. If it is, we throw a new instance of BankAccountException with the message "Withdrawal amount exceeds available balance" using the throw keyword.

4. If the amount is less than or equal to the balance, we subtract the amount from the balance.

By implementing the BankAccountException class and modifying the withdraw method as mentioned, we can handle the case where the withdrawal amount exceeds the available balance and throw the custom exception accordingly.