Java Exception Hierarchy

Overview of Exception Hierarchy

• Object Class: Top of the class hierarchy in Java.
  • Note: Every class in Java extends Object class, even if not explicitly mentioned.

Throwable Class

• Throwable: A superclass for exceptions and errors.
  • Exception Class: Extends Throwable and is the main focus.
  • Error Class: Also extends Throwable, but not discussed as much.

Exception vs Error

• Exceptions: Can be handled by the programmer.
• Errors: Generally not handleable; they indicate serious problems that a reasonable application should not try to catch.
  • Examples of errors include:
    • Thread Death: What happens if a thread dies unexpectedly?
    • I/O Errors: Issues during input/output operations.
    • Virtual Machine Errors: E.g., OutOfMemoryError when memory is insufficient.

Exception Class Hierarchy

• Runtime Exception: A subclass of Exception that can be handled, but is not mandatory.

  • Examples:
    • ArithmeticException: Error in arithmetic operations.
    • IndexOutOfBoundsException: Accessing an index not available in an array or collection.
    • NullPointerException: Attempting to use an object reference that has the null value.
  • These exceptions are termed as Unchecked Exceptions.

• Checked Exceptions: These must be handled explicitly in the code.

  • Examples include:
    • SQLException: Issues related to database access.
    • IOException: Errors while performing input/output operations.
  • The compiler enforces handling these exceptions.
    • Example: When using Class.forName(), it throws IOException, necessitating handling.

Summary of Exception Handling

• Unchecked Exceptions: Handled at the programmer's discretion.
• Checked Exceptions: Compiler mandates handling of these exceptions.
• As a best practice, programmers should handle exceptions to maintain client satisfaction.

Conclusion

• Understanding the hierarchy helps determine which exceptions you need to manage and which can be ignored.
• Good programming practice involves handling exceptions to ensure reliable and robust applications.