Exception Handling — Java Tutorial

Try-Catch-Finally

Exception handling prevents your program from crashing when errors occur. Use try-catch to handle exceptions gracefully.

Example

try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println("Cannot divide by zero: " + e.getMessage());
} finally {
    System.out.println("This always runs.");
}

// Multiple catch blocks
try {
    String text = null;
    text.length();  // NullPointerException
} catch (NullPointerException e) {
    System.out.println("Null reference!");
} catch (Exception e) {
    System.out.println("General error: " + e.getMessage());
}

// Try-with-resources (auto-closeable)
try (Scanner scanner = new Scanner(System.in)) {
    String input = scanner.nextLine();
} // scanner is automatically closed

Custom Exceptions

Create custom exception classes for application-specific error handling.

Example

// Custom exception
public class InsufficientFundsException extends Exception {
    private double amount;

    public InsufficientFundsException(double amount) {
        super("Insufficient funds. Needed: $" + amount);
        this.amount = amount;
    }

    public double getAmount() { return amount; }
}

// Throwing custom exception
public void withdraw(double amount) throws InsufficientFundsException {
    if (amount > balance) {
        throw new InsufficientFundsException(amount - balance);
    }
    balance -= amount;
}

// Catching custom exception
try {
    account.withdraw(1000);
} catch (InsufficientFundsException e) {
    System.out.println(e.getMessage());
}