When should you use wait and notify instead of higher-level Java concurrency tools?

Notification is not durable: a signal sent before a thread begins waiting is not stored for later, so the shared condition state is the real truth. Complex protocols are vulnerable to lost progress, starvation, and shutdown bugs. I include interruption and termination states in the same guarded loop and test several producers, consumers, and shutdown races. If the protocol takes a diagram to explain, a queue or explicit state owner is usually easier to maintain.