Last-mile 1Z0-830 review: high-yield Java 21 rules and code patterns for generics, collections, streams, exceptions, and concurrency fundamentals.
Use this for last‑mile review. The exam rewards “small correctness details”.
| Pattern | What it means |
|---|---|
List<? extends T> | you can read T (or subtype); you can’t add T safely |
List<? super T> | you can add T; reads come back as Object |
1var names = people.stream()
2 .filter(p -> p.age() >= 18)
3 .map(Person::name)
4 .toList();
1var byDept = employees.stream()
2 .collect(Collectors.groupingBy(Employee::department));
AutoCloseable.1try (var in = Files.newInputStream(path)) {
2 // ...
3}