এক্সেপশন হ্যান্ডলিং (Exception Handling)

public class Main {
    public static void main(String[] args) {
        // Basic try-catch
        try {
            int result = 10 / 0;  // this will throw ArithmeticException
            System.out.println("Result: " + result);  // never reached
        } catch (ArithmeticException e) {
            System.out.println("Oops! Can't divide by zero.");
            System.out.println("Error: " + e.getMessage());
        }

        System.out.println("---");

        // Multiple catch blocks
        String[] names = {"Anika", "Rafi"};
        try {
            System.out.println(names[5]);  // out of bounds!
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("That index doesn't exist!");
        } catch (Exception e) {
            System.out.println("Something else went wrong.");
        }

        System.out.println("---");

        // Finally — runs NO MATTER WHAT
        try {
            int x = Integer.parseInt("abc");  // NumberFormatException
        } catch (NumberFormatException e) {
            System.out.println("That's not a number!");
        } finally {
            System.out.println("Finally block always runs.");
        }

        System.out.println("Program continues normally!");
    }
}

Oops! Can't divide by zero.
Error: / by zero
---
That index doesn't exist!
---
That's not a number!
Finally block always runs.
Program continues normally!

public class Main {
    // Custom exception
    static class InvalidAgeException extends Exception {
        InvalidAgeException(String message) {
            super(message);
        }
    }

    // Method that throws our custom exception
    static void setAge(String name, int age) throws InvalidAgeException {
        if (age < 0) {
            throw new InvalidAgeException("Age can't be negative: " + age);
        }
        if (age > 150) {
            throw new InvalidAgeException("Age seems unrealistic: " + age);
        }
        System.out.println(name + "'s age set to " + age);
    }

    // Method that throws a built-in exception
    static double divide(double a, double b) {
        if (b == 0) {
            throw new IllegalArgumentException("Cannot divide by zero!");
        }
        return a / b;
    }

    public static void main(String[] args) {
        // Handle custom exception
        try {
            setAge("Anika", 25);
            setAge("Rafi", -5);
        } catch (InvalidAgeException e) {
            System.out.println("Error: " + e.getMessage());
        }

        System.out.println("---");

        // Handle built-in exception
        try {
            System.out.println("10 / 3 = " + divide(10, 3));
            System.out.println("10 / 0 = " + divide(10, 0));
        } catch (IllegalArgumentException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

Anika's age set to 25
Error: Age can't be negative: -5
---
10 / 3 = 3.3333333333333335
Error: Cannot divide by zero!

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Try-with-resources automatically closes resources
        // Even if an exception occurs!
        String data = "42\n3.14\nhello\n100";

        try (Scanner scanner = new Scanner(data)) {
            while (scanner.hasNext()) {
                String token = scanner.next();
                try {
                    int num = Integer.parseInt(token);
                    System.out.println("Integer: " + num);
                } catch (NumberFormatException e1) {
                    try {
                        double d = Double.parseDouble(token);
                        System.out.println("Double: " + d);
                    } catch (NumberFormatException e2) {
                        System.out.println("String: " + token);
                    }
                }
            }
        }  // scanner is automatically closed here!

        System.out.println("Scanner was auto-closed. Clean!");
    }
}

Integer: 42
Double: 3.14
String: hello
Integer: 100
Scanner was auto-closed. Clean!