Exception Handling

Throwable
├── Error (JVM issues — don't catch these)
│   ├── OutOfMemoryError
│   └── StackOverflowError
└── Exception
    ├── IOException (Checked)
    ├── SQLException (Checked)
    └── RuntimeException (Unchecked)
        ├── NullPointerException
        ├── ArrayIndexOutOfBoundsException
        ├── ArithmeticException
        └── ClassCastException

try {
    int result = 10 / 0; // ArithmeticException
} catch (ArithmeticException e) {
    System.out.println("Error: Cannot divide by zero!");
    System.out.println("Details: " + e.getMessage());
}

try {
    int[] arr = {1, 2, 3};
    System.out.println(arr[10]); // ArrayIndexOutOfBoundsException
} catch (ArithmeticException e) {
    System.out.println("Math error");
} catch (ArrayIndexOutOfBoundsException e) {
    System.out.println("Array index error");
} catch (Exception e) {
    System.out.println("General error: " + e.getMessage());
}

try {
    // risky code
} catch (Exception e) {
    // handle error
} finally {
    System.out.println("This ALWAYS runs.");
}

public static void validateAge(int age) throws IllegalArgumentException {
    if (age < 0) {
        throw new IllegalArgumentException("Age cannot be negative!");
    }
}

class InsufficientFundsException extends Exception {
    private double amount;
    public InsufficientFundsException(double amount) {
        super("Insufficient funds. Short by: $" + amount);
        this.amount = amount;
    }
}

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

try (Scanner sc = new Scanner(System.in)) {
    String input = sc.nextLine();
} // Scanner automatically closed here

import java.util.Scanner;
import java.util.InputMismatchException;

public class SafeCalculator {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        try {
            System.out.print("Enter numerator: ");
            int a = sc.nextInt();
            System.out.print("Enter denominator: ");
            int b = sc.nextInt();
            System.out.println("Result: " + (a / b));
        } catch (ArithmeticException e) {
            System.out.println("Error: Cannot divide by zero!");
        } catch (InputMismatchException e) {
            System.out.println("Error: Please enter valid integers!");
        } finally {
            System.out.println("Calculator session ended.");
            sc.close();
        }
    }
}