Exception Definition

An unexpected problem/event that occurs during the execution of a program (Runtime) which stops the normal flow. • Root Class: java.lang.Throwable. • Object Class: Parent of Throwable.

Hierarchy

Throwable

1. Error (Hardware/System level, e.g., StackOverflowError).
2. Exception:

• Checked (Compile-time): Compiler forces handling (e.g., FileNotFoundException, IOException). • Unchecked (Runtime): Compiler ignores (e.g., ArithmeticException, NullPointerException). • Note: RuntimeException and its children are Unchecked. All others are Checked.

Exception Handling Keywords

1. try: Block consisting of code that might raise an exception.
2. catch: Block used to handle the exception thrown by try.

• Can have multiple catch blocks (Child first, Parent last).

3. finally: Block that always executes (even if exception occurs or handled).

• Used for resource cleanup (Closing DB, Streams).

4. throw: Used to explicitly throw an exception object. throw new ArithmeticException("Msg");
5. throws: Used in method signature to declare/propagate checked exceptions. void m() throws IOException

Exception Propagation

Movement of exception object from called method to calling method. Unchecked exceptions propagate automatically. Checked exceptions need throws.

Custom Exception

User defined exceptions.

1. Checked: Extend Exception.
2. Unchecked: Extend RuntimeException.