Working with Arrays and Collections →mediumMultiple ChoiceObjective-mapped

1Z0-829 Working with Arrays and Collections Practice Question

A method returns a List<Integer>. The caller wants to ensure the list cannot be modified. Which is the best approach?

⚠ Common exam trap

Many candidates 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.

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 Collections.unmodifiableList(list);

`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.

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 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.

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1Z0-829 Working with Arrays and Collections Practice Question

Why each option matters

Option-by-option breakdown

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