Exceptions, Assertions & Logging

Exception Doctrine (EJ 69–77)

Effective Java's chapter 10, condensed: exceptions only for exceptional conditions, checked only when callers can recover, standard types over custom, translation at layer boundaries, documentation and failure-capture always, atomicity where possible.

Avoid unnecessary checked exceptions — they tax every caller (EJ 71)
Document every exception thrown, with @throws (EJ 74)
Detail messages must capture the values that caused the failure (EJ 75)
Strive for failure atomicity: a failed call should leave the object as it was (EJ 76)
Never let an exception escape with less information than it arrived with

The doctrine at a glance
Item	Rule
69	Use exceptions only for exceptional conditions — never control flow
70	Checked for recoverable conditions; runtime for programming errors
71	Avoid unnecessary checked exceptions (consider Optional or state-testing)
72	Favor standard exceptions (IAE, ISE, NPE, UOE…)
73	Throw exceptions appropriate to the abstraction (translate + chain)
74	Document all exceptions thrown by each method
75	Include failure-capture information in detail messages
76	Strive for failure atomicity
77	Don't ignore exceptions

Failure-capture in messages (EJ Item 75)

// Useless:  throw new IndexOutOfBoundsException();
// Useful — carries every value needed to reproduce:
throw new IndexOutOfBoundsException(
        "index " + index + " out of bounds for range [" + lower + ", " + upper + ")");

Failure atomicity (EJ 76): validate parameters before mutating (Stack.pop checks emptiness before decrementing), order operations so mutation comes last, or work on a copy and swap in on success. Callers who catch your exception will reasonably assume the object is still usable — make that true.

On checked-exception cost (EJ 71): a checked exception forces try/catch or throws on every transitive caller and breaks lambda-based composition (Functional Interfaces). Reserve it for cases where the caller genuinely can recover and no better design (Optional return, state-testing method) exists. When in doubt, unchecked.