Object-Oriented Programming in Java

Exception Handling Fundamentals

An exception is an event that disrupts the normal flow of the program. Java uses a robust, object-oriented model for error handling.

• Exception – indicates runtime errors that can be handled
• Error – serious issues not expected to be handled (e.g. OutOfMemoryError)
• All exceptions derive from the class Throwable

The main advantage of Java's exception system is **separation of error-handling code from normal logic**.

Diagram: exception-hierarchy.png

Types of Exceptions

• Checked exceptions – must be caught or declared (IOException, SQLException)
• Unchecked exceptions – inherit from RuntimeException (ArithmeticException, NullPointerException)
• Errors – not meant to be handled (StackOverflowError)

int x = 10 / 0;   // ArithmeticException

FileReader fr = new FileReader("abc.txt");   // must be handled

Using try, catch, and finally

A try block contains statements that may throw an exception.catch blocks handle the specific exception types. The finally block executes whether or not an exception occurs.

try {
  int a = 5 / 0;
} catch (ArithmeticException e) {
  System.out.println("Cannot divide by zero");
} finally {
  System.out.println("Cleanup operations");
}

• Use multiple catch blocks for multiple exception types
• finally is often used to close files, connections, or release resources

throw and throws

throw explicitly throws an exception.throws declares that a method may throw an exception.

void checkAge(int age) {
  if(age < 18)
    throw new IllegalArgumentException("Too young");
}

void readFile() throws IOException {
  FileReader f = new FileReader("data.txt");
}

Java’s Built-in Exceptions

Commonly asked in exams:

• ArithmeticException
• ArrayIndexOutOfBoundsException
• NullPointerException
• NumberFormatException
• IOException

Creating Custom Exceptions

User-defined exceptions extend the Exception class.

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

void check(int m) throws InvalidMarksException {
  if(m < 0 || m > 100)
    throw new InvalidMarksException("Invalid marks");
}

Summary

Exception handling improves program reliability by allowing controlled error management. Using try-catch-finally, throwing exceptions, and understanding the exception class hierarchy are essential skills for robust Java development.

Diagrams to insert: try-catch-flowchart.png, exception-types-table.png