1Z0-829 Working with Arrays and Collections Practice Question
Which TWO statements are true about creating an unmodifiable List?
⚠ Common exam trap
A common mix-up: candidates confuse 'unmodifiable view' (where the backing list can still change) with 'immutable list' (where the list itself cannot change at all), leading them to incorrectly think `Collections.unmodifiableList()` makes the backing list safe from all modifications.
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() returns a view that is unmodifiable, but the backing list can still be changed.
A is correct because `Collections.unmodifiableList()` returns a view of the backing list that cannot be modified through the returned reference, but any changes made to the original backing list are reflected in the view. This means the view is unmodifiable but not immutable, as the underlying list can still be mutated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Collections.unmodifiableList() returns a view that is unmodifiable, but the backing list can still be changed.
Why this is correct
View is unmodifiable, backing list change reflected.
- ✓
List.of() returns an immutable list that does not support any modification.
Why this is correct
Truly immutable.
- ✗
List.copyOf() creates a list that, if the source list is changed, the copy also changes.
Why it's wrong here
copyOf creates independent immutable copy.
- ✗
new ArrayList<>(Arrays.asList(...)) creates an unmodifiable list.
Why it's wrong here
ArrayList is mutable.
- ✗
Arrays.asList() returns an unmodifiable list.
Why it's wrong here
Returns fixed-size but modifiable via set().
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