Question 441 of 513
1Z0-829 Working with Arrays and Collections Practice Question
Given: HashSet<String> set = new HashSet<>(); set.add("A"); set.add("B"); set.add("C"); set.add("A"); System.out.println(set.size()); What is the output?
⚠ Common exam trap
The trap here is that candidates may forget that Set collections (unlike List) inherently reject duplicates, leading them to count all add() calls including the duplicate "A" and choose 4.
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
✓
3
HashSet does not allow duplicate elements. When adding "A" twice, the second add is ignored, so the set contains only three unique elements: "A", "B", and "C". Therefore, set.size() returns 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.
- ✗
Compilation fails
Why it's wrong here
Code compiles fine.
- ✓
3
Why this is correct
Correct, only unique elements counted.
- ✗
4
Why it's wrong here
Incorrect; duplicates are ignored.
- ✗
2
Why it's wrong here
Incorrect; there are three unique elements.
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Last reviewed: Jun 11, 2026
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