This 1Z0-829 practice question tests your understanding of working with arrays and collections. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A method returns a List<Integer>. The caller wants to ensure the list cannot be modified. Which is the best approach?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
return Arrays.asList(list.toArray());
Why wrong: Returns a mutable list backed by array.
return new ArrayList<>(list);
Why wrong: Mutable copy.
return (List<Integer>) list.clone();
Why wrong: clone() returns mutable list.
return Collections.unmodifiableList(list);
Returns an unmodifiable view.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
return Collections.unmodifiableList(list);
Option D is correct because `Collections.unmodifiableList()` returns a read-only view of the specified list. Any attempt to modify the returned list (e.g., via `add`, `remove`, `set`) will throw an `UnsupportedOperationException`. This is the standard, recommended approach in the Java Collections Framework to provide an unmodifiable wrapper without copying the underlying data.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
return Arrays.asList(list.toArray());
Why it's wrong here
Returns a mutable list backed by array.
return new ArrayList<>(list);
Why it's wrong here
Mutable copy.
return (List<Integer>) list.clone();
Why it's wrong here
clone() returns mutable list.
return Collections.unmodifiableList(list);
Why this is correct
Returns an unmodifiable view.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often confuse 'unmodifiable view' with 'immutable copy' and may pick options like `Arrays.asList()` or `clone()` thinking they prevent modification, but those still allow structural changes or mutation through the backing array.
Detailed technical explanation
`Collections.unmodifiableList()` returns a view that delegates read operations to the backing list but throws `UnsupportedOperationException` on mutating operations. Note that if the original list is later modified, the unmodifiable view reflects those changes. For a truly immutable list (since Java 9), use `List.copyOf()` or `List.of()`, which create a copy that cannot be changed and also disallow null elements.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the 1Z0-829 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
Working with Arrays and Collections — This question tests Working with Arrays and Collections — Read the scenario before looking for a memorised answer..
The correct answer is: return Collections.unmodifiableList(list); — Option D is correct because `Collections.unmodifiableList()` returns a read-only view of the specified list. Any attempt to modify the returned list (e.g., via `add`, `remove`, `set`) will throw an `UnsupportedOperationException`. This is the standard, recommended approach in the Java Collections Framework to provide an unmodifiable wrapper without copying the underlying data.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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