- A
Arrays.asList("a", "b")
Why wrong: Returns fixed-size but mutable via set.
- B
List.of(List.of("a", "b"))
Why wrong: Creates a list containing a list, not a flat immutable list.
- C
Collections.unmodifiableList(new ArrayList<>(List.of("a", "b")))
Wraps list to be unmodifiable.
- D
List.copyOf(Arrays.asList("a", "b"))
List.copyOf returns an immutable list.
- E
new ArrayList<>(List.of("a", "b"))
Why wrong: Creates a mutable ArrayList.
Question 206 of 519
1Z0-829 Working with Arrays and Collections Practice Question
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.
Which TWO are valid ways to create an immutable list in Java 17? (Choose two.)
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
✓
Collections.unmodifiableList(new ArrayList<>(List.of("a", "b")))
Option C is correct because `Collections.unmodifiableList()` wraps a mutable list in an unmodifiable view, preventing any structural modifications. Option D is correct because `List.copyOf()` creates an immutable list from an existing collection, throwing `NullPointerException` if any element is null. Both produce lists that cannot be modified after creation.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Arrays.asList("a", "b")
Why it's wrong here
Returns fixed-size but mutable via set.
- ✗
List.of(List.of("a", "b"))
Why it's wrong here
Creates a list containing a list, not a flat immutable list.
- ✓
Collections.unmodifiableList(new ArrayList<>(List.of("a", "b")))
Why this is correct
Wraps list to be unmodifiable.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
List.copyOf(Arrays.asList("a", "b"))
Why this is correct
List.copyOf returns an immutable list.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
new ArrayList<>(List.of("a", "b"))
Why it's wrong here
Creates a mutable ArrayList.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Oracle often tests the distinction between an unmodifiable view (which can be circumvented if the backing list is accessible) and a truly immutable list (which cannot be changed by any means), and candidates mistakenly think `Arrays.asList()` or `new ArrayList<>()` are immutable.
Detailed technical explanation
How to think about this question
Under the hood, `List.copyOf()` (introduced in Java 10) returns an unmodifiable list that is not a view — it copies the elements into a new internal array, guaranteeing immutability even if the source list is later modified. `Collections.unmodifiableList()` returns a wrapper that delegates all mutator methods to throw `UnsupportedOperationException`, but the underlying mutable list can still be changed through its reference, breaking the immutability contract. In real-world scenarios, prefer `List.of()` or `List.copyOf()` for true immutability, especially in concurrent or API design contexts.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this 1Z0-829 question test?
Working with Arrays and Collections — This question tests Working with Arrays and Collections — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Collections.unmodifiableList(new ArrayList<>(List.of("a", "b"))) — Option C is correct because `Collections.unmodifiableList()` wraps a mutable list in an unmodifiable view, preventing any structural modifications. Option D is correct because `List.copyOf()` creates an immutable list from an existing collection, throwing `NullPointerException` if any element is null. Both produce lists that cannot be modified after creation.
What should I do if I get this 1Z0-829 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
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