1Z0-829 Java 17 Wildcards, Collections, and Algorithms Guide
April 13, 2026
Study 1Z0-829 Java 17 Wildcards, Collections, and Algorithms: key concepts, common traps, and exam decision cues.
Generics and collections questions are usually won before runtime if you classify the type relationship and the collection contract correctly.
Generic-and-collection map
| If the stem is mainly about… |
Better first instinct |
| source-only reading |
? extends T may be the right direction |
| sink-only writing |
? super T may be the right direction |
| exact generic container type |
remember invariance |
| collection result or mutation |
identify mutability and ordering first |
| custom ordering |
comparator contract matters |
What the exam is really testing
| If the code shows… |
Strong reading |
List<Number> vs List<Integer> |
generic invariance is likely the point |
List.of(...) or Arrays.asList(...) |
collection contract is the real issue |
Comparable or Comparator use |
ordering behavior and legality matter |
Common traps
| Trap |
Better rule |
believing List<Integer> is a subtype of List<Number> |
generic invariance blocks that |
| treating all lists as fully mutable |
factory and wrapper methods change the contract |
| using wildcard intuition instead of PECS |
read and write safety should be explicit |
Quiz
Loading quiz…
Revised on Sunday, May 10, 2026