Working with Arrays and Collections →mediumMultiple ChoiceObjective-mapped

1Z0-829 Working with Arrays and Collections Practice Question

Given: TreeSet<Integer> set = new TreeSet<>(List.of(3,1,2)); set.add(2); System.out.println(set); What is the output?

⚠ Common exam trap

Many candidates confuse TreeSet with HashSet or List, expecting insertion order or allowing duplicates, but TreeSet enforces sorted order and uniqueness via its underlying tree structure.

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

✓

[1,2,3]

E is correct because TreeSet maintains elements in their natural sorted order (ascending for integers). The list [3,1,2] is sorted to [1,2,3], and adding 2 again has no effect since TreeSet does not allow duplicates. The output is [1,2,3].

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
[1,2]
Why it's wrong here
Incorrect: all three distinct elements are present.
✗
[1,3,2]
Why it's wrong here
Incorrect: order is not this.
✗
[3,1,2]
Why it's wrong here
Incorrect: TreeSet sorts elements.
✗
UnsupportedOperationException
Why it's wrong here
Incorrect: no exception occurs.
✓
[1,2,3]
Why this is correct
Correct: sorted order, duplicates ignored.

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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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