Exception Handling: Robustness, Recovery & Fault Tolerance

/**
 * DevAscent Academy — Unit 7 Capstone Project
 * Demonstrates Checked/Unchecked Exceptions, Custom Exceptions, and Try-Catch-Finally.
 */

// 1. Custom Checked Business Domain Exception
class InsufficientFundsException extends Exception {
    private final double deficit;

    public InsufficientFundsException(String message, double deficit) {
        super(message);
        this.deficit = deficit;
    }

    public double getDeficit() { return this.deficit; }
}

// 2. Banking Ledger Service
public class ResilientBankingEngine {
    private double balance = 1000.00;

    // Method declaring checked exception via 'throws'
    public void withdraw(String amountInput) throws InsufficientFundsException {
        System.out.println("Processing Withdrawal Request for: '" + amountInput + "'");

        double parsedAmount;
        try {
            // May throw NumberFormatException (Unchecked)
            parsedAmount = Double.parseDouble(amountInput);
        } catch (NumberFormatException nfe) {
            System.out.println("  [ERROR] Malformed numeric input! Aborting transaction.");
            return;
        }

        try {
            if (parsedAmount > this.balance) {
                double shortBy = parsedAmount - this.balance;
                // Explicitly trigger custom checked exception via 'throw'
                throw new InsufficientFundsException("Overdraft Limit Exceeded.", shortBy);
            }

            this.balance -= parsedAmount;
            System.out.printf("  [SUCCESS] Dispensed: $%.2f | Remaining Balance: $%.2f%n", 
                    parsedAmount, this.balance);

        } finally {
            // Guaranteed cleanup audit logger
            System.out.println("  [FINALLY AUDIT] Ledger snapshot completed. DB connection released.");
        }
    }

    public static void main(String[] args) {
        System.out.println("==================================================");
        System.out.println("   DEVASCENT RESILIENT BANKING TRANSACTION DEMO   ");
        System.out.println("==================================================");

        ResilientBankingEngine atm = new ResilientBankingEngine();

        // Test Case 1: Valid Withdrawal
        try {
            atm.withdraw("300.00");
        } catch (InsufficientFundsException e) {
            System.out.println("Caught exception: " + e.getMessage());
        }
        System.out.println("--------------------------------------------------");

        // Test Case 2: Malformed Input (NumberFormatException handled gracefully)
        try {
            atm.withdraw("one_hundred_usd");
        } catch (InsufficientFundsException e) {
            System.out.println("Caught exception: " + e.getMessage());
        }
        System.out.println("--------------------------------------------------");

        // Test Case 3: Overdraft Custom Checked Exception
        try {
            atm.withdraw("2500.00");
        } catch (InsufficientFundsException ife) {
            System.out.printf("  [HANDLED CUSTOM] %s (Deficit Amount: $%.2f)%n", 
                    ife.getMessage(), ife.getDeficit());
        }
        System.out.println("==================================================");
    }
}