1. Introduction to Exception Handling

1.1 What is an Exception

An exception is an event that disrupts the normal flow of a program during execution.

1.2 Errors vs Exceptions

Errors → Serious issues (system-level)
Exceptions → Can be handled in code

1.3 Why Exception Handling

Prevents program crash
Maintains normal flow
Improves reliability

1.4 Example

int a = 10;
int b = 0;
System.out.println(a / b); // ArithmeticException

2. Types of Exceptions

2.1 Checked Exceptions

Checked at compile time
Example: IOException

2.2 Unchecked Exceptions

Occur at runtime
Example: NullPointerException

2.3 Errors

Not handled by program
Example: OutOfMemoryError

2.4 Common Exceptions

ArithmeticException
NullPointerException
ArrayIndexOutOfBoundsException

3. try, catch, finally

3.1 try Block

Contains code that may cause exception.

3.2 catch Block

Handles exception.

3.3 finally Block

Always executes (optional).

3.4 Example

try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println("Error occurred");
} finally {
    System.out.println("Done");
}

3.5 Multiple catch

try {
    // code
} catch (ArithmeticException e) {
} catch (NullPointerException e) {
}

4. throw and throws

4.1 throw Keyword

Used to explicitly throw an exception.

throw new ArithmeticException("Error");

4.2 throws Keyword

Declares exceptions in method.

void readFile() throws IOException {
}

4.3 Difference

throw	throws
Used inside method	Used in method declaration
Throws one exception	Can declare multiple

5. Creating Custom Exceptions

5.1 Definition

User-defined exceptions.

5.2 Steps

Extend Exception class
Create constructor
Use throw

5.3 Example

class MyException extends Exception {
    MyException(String msg) {
        super(msg);
    }
}

5.4 Using Custom Exception

void checkAge(int age) throws MyException {
    if (age < 18) {
        throw new MyException("Not eligible");
    }
}

Conclusion

Exception handling is essential for building robust Java applications. By properly handling errors using try-catch blocks and creating custom exceptions, developers can ensure their programs run smoothly even in unexpected situations. Mastering this concept is crucial for real-world application development.

Exception Handling