A stream self-check tests lazy demand, one-use pipelines, encounter order and reduction contracts.
Review the contracts
Review stream execution, reduction contracts, gatherer state before answering.
Choose and explain an answer
Identify the terminal operation and any state shared across callbacks. Decide whether the result depends on ordering or a valid associative reduction.
Select an answer for every question, then check the result and read each explanation. Progress remains in this browser; this is a self-check, not a judged program submission or a credential.
Common Mistakes
A stream is not a cached collection. Parallel execution does not repair shared mutable state or an invalid reduction rule.