Custom InsufficientBalanceException

Create a checked exception InsufficientBalanceException and a BankAccount whose withdraw(amount) throws it when amount > balance. On success, subtract and return the new balance.

Interview angle

Interviewers want to see when you choose checked vs unchecked, and that the exception carries a useful message (requested amount + current balance).

Starter code

class InsufficientBalanceException extends Exception {
    // TODO
}

class BankAccount {
    private double balance;

    BankAccount(double balance) { this.balance = balance; }

    public double withdraw(double amount) throws InsufficientBalanceException {
        // TODO
        return 0;
    }
}

public class BankDemo {
    public static void main(String[] args) {
        BankAccount a = new BankAccount(1000);
        try {
            System.out.println(a.withdraw(1500));
        } catch (InsufficientBalanceException e) {
            System.out.println(e.getMessage());
        }
    }
}

Solution

class InsufficientBalanceException extends Exception {
    InsufficientBalanceException(String message) {
        super(message);
    }
}

class BankAccount {
    private double balance;

    BankAccount(double balance) { this.balance = balance; }

    public double withdraw(double amount) throws InsufficientBalanceException {
        if (amount > balance) {
            throw new InsufficientBalanceException(
                "Need " + amount + " but balance is " + balance
            );
        }
        balance -= amount;
        return balance;
    }
}

public class BankDemo {
    public static void main(String[] args) {
        BankAccount a = new BankAccount(1000);
        try {
            System.out.println(a.withdraw(1500));
        } catch (InsufficientBalanceException e) {
            System.out.println(e.getMessage());
        }
    }
}