At the top is the Throwable class, which has two main subclasses:

• Exception → Represents conditions that programs should handle.
• Error → Represents serious problems that applications should not handle (e.g., OutOfMemoryError).

Exception further splits into:

• Checked exceptions (compile-time) – e.g., IOException, SQLException.
• Unchecked exceptions (runtime) – e.g., NullPointerException, ArithmeticException.

• Error: Irrecoverable conditions (e.g., JVM crash, OutOfMemoryError).
• Exception: Conditions programs can catch and handle.

• Checked exceptions: Must be declared or handled in code. Compiler enforces it. Example: IOException.
• Unchecked exceptions: Not required to be declared or handled. Example: NullPointerException.

Because it extends RuntimeException, which is a subclass of Exception but not enforced by the compiler. It represents programming errors like null access or division by zero.

Yes, by creating a custom exception class extending Exception (checked) or RuntimeException (unchecked).