Exception handling in Java is a mechanism to handle runtime errors so that the normal flow of a program is not interrupted.

Types of Exceptions in Java

✅ Checked Exception (Compile-time Exception)

Must be handled at compile time.
Example: IOException, SQLException.

⚠️ Unchecked Exception (Runtime Exception)

Occurs at runtime and is not mandatory to handle.
Example: NullPointerException, ArithmeticException.

❌ Error

Cannot be handled by the program.
Example: OutOfMemoryError, StackOverflowError.

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🔑 Key Exception Handling Constructs

🔹 try

A block of code where an exception may occur.

🔹 catch

A block to handle exceptions.

🔹 finally

This block will execute whether an exception occurs or not.

🔹 throws

Used in method signatures to declare exceptions that may be thrown.

🔹 throw

Used to explicitly throw an exception.

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🎯 Class Hierarchy:

• Checked Exception: extends Exception
• Unchecked Exception: extends RuntimeException

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📌 Java Code Snippets

1️⃣ Try-Catch Example

📌 Description: Demonstrates handling exceptions with a try-catch block.

try {
    int x = 10;
    int y = 0;
    int result = x / y; // This will throw an ArithmeticException
} catch (ArithmeticException e) {
    System.out.println("Cannot divide by zero!");
}

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2️⃣ Custom Exception Handling Example

📌 Description: Demonstrates creating and using custom exceptions.

class InvalidAgeException extends Exception {
    public InvalidAgeException(String message) {
        super(message);
    }
}

void validateAge(int age) throws InvalidAgeException {
    if (age < 18) {
        throw new InvalidAgeException("Age must be 18 or older");
    }
}

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3️⃣ Finally Block Execution Example

📌 Description: The finally block executes even if an exception occurs.

try {
    System.out.println(10 / 0);
} catch (ArithmeticException e) {
    System.out.println("Exception caught");
} finally {
    System.out.println("Finally block executed");
}

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❓ Interview Questions

1️⃣ What is Exception Handling in Java?

📌 Answer: Exception handling is a mechanism to handle runtime errors, ensuring the normal flow of a program.

2️⃣ What is the difference between throw and throws?

📌 Answer:

• throw: Used inside a method to explicitly throw an exception.
• throws: Declares exceptions that may be thrown by a method.

Example:

void check(int age) throws InvalidAgeException {
    if (age < 18) {
        throw new InvalidAgeException("Underage!");
    }
}

3️⃣ What happens if an exception is not caught?

📌 Answer: If an exception is not caught, the JVM terminates the program and prints the stack trace.

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🔹 Important Notes:

• If you have a return statement inside a try block, the finally block will still execute.
• System.exit(0); prevents the finally block from executing.