Question 485 of 513
1Z0-829 Working with Arrays and Collections Practice Question
A developer is designing a method that returns an immutable list of strings from an array. Which approach best follows current Java best practices?
⚠ Common exam trap
It's easy for candidates to confuse `Arrays.asList()` (which returns a mutable, array-backed list) with an immutable list, or they think `Collections.unmodifiableList()` provides full immutability, but it only prevents modification through the returned reference while the underlying array remains mutable.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Return List.of(array)
`List.of(array)` returns an immutable list that is null-hostile and structurally immutable, as specified by the Java Platform Module System (JPMS) and the `List` interface since Java 9. This approach aligns with current best practices by providing a concise, safe, and predictable immutable collection without the overhead of wrapping or defensive copying.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Return new ArrayList<>(Arrays.asList(array))
Why it's wrong here
Returns a mutable list; not immutable.
- ✗
Return Collections.unmodifiableList(Arrays.asList(array))
Why it's wrong here
This works but is verbose and still allows nulls; List.of is preferred.
- ✗
Return Arrays.asList(array)
Why it's wrong here
Arrays.asList returns a fixed-size list that is mutable via set() and allows nulls, so it is not immutable.
- ✓
Return List.of(array)
Why this is correct
List.of returns an immutable list, introduced in Java 9, and rejects nulls, making it the best practice.
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Last reviewed: Jul 4, 2026
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