Exception Handling

Exception Handling

Java uses exceptions to handle errors at runtime. When something goes wrong, an exception is thrown, and you can catch it to handle it gracefully.

try / catch / finally

try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println("Error: " + e.getMessage());
} finally {
    System.out.println("This always runs");
}

• try — wraps code that might throw an exception
• catch — handles a specific exception type
• finally — always executes, whether an exception occurred or not (useful for cleanup)

Checked vs Unchecked Exceptions

• Unchecked (RuntimeException and its subclasses): NullPointerException, ArithmeticException, ArrayIndexOutOfBoundsException. The compiler does not force you to handle these.
• Checked (Exception but not RuntimeException): IOException, SQLException. The compiler forces you to either catch them or declare them with throws.

Throwing Exceptions

Use throw to raise an exception yourself:

void setAge(int age) {
    if (age < 0) {
        throw new IllegalArgumentException("Age cannot be negative");
    }
}

Custom Exceptions

You can define your own exception classes by extending Exception (checked) or RuntimeException (unchecked):

class InsufficientFundsException extends RuntimeException {
    private double deficit;

    InsufficientFundsException(double deficit) {
        super("Insufficient funds: need " + deficit + " more");
        this.deficit = deficit;
    }

    double getDeficit() { return deficit; }
}

Your Task

Create a static inner class SafeCalculator with:

• static String divide(int a, int b) — returns the result as a string, or "Error: division by zero" if b is 0 (use try/catch on ArithmeticException)
• static String parseAndAdd(String x, String y) — parses both strings as integers and returns their sum as a string. If either string is not a valid integer, return "Error: invalid number". Use a finally block to print "parse complete" regardless of outcome.

Also create a custom exception class NegativeNumberException (extending RuntimeException) with a constructor that takes a String message, and a method:

• static int squareRoot(int n) — if n < 0, throw NegativeNumberException with message "negative input: " followed by n. Otherwise return (int) Math.sqrt(n).

Then run the test sequence shown in the expected output.