Frequently asked questions for Java SE 21 Developer Professional (1Z0-830): prerequisites, difficulty, what to focus on, and study strategy.
Not necessarily, but you do need hands-on practice. If you can read code quickly, spot type/flow issues, and write small programs using collections/streams and exceptions, you’re in good shape.
Generics + collections + streams. Many questions combine them (wildcards, inference, map/filter/collect behavior, and mutability).
Choosing answers that “look right” but violate Java’s rules: incorrect wildcard bounds, wrong overload selection, mistaken exception flow, or assuming a collection/stream operation mutates the source.
Treat this exam like a coding interview: write short snippets, predict the output/compile errors, then verify. Make flashcards for rules that repeatedly surprise you.