Question 1hardmultiple choice
Full question →- A
Compilation fails
Why wrong: Code compiles fine.
- B
3
Correct, only unique elements counted.
- C
4
Why wrong: Incorrect; duplicates are ignored.
- D
2
Why wrong: Incorrect; there are three unique elements.
Question 432 of 509
1Z0-829 Working with Arrays and Collections Practice Question
This 1Z0-829 practice question tests your understanding of working with arrays and collections. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
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?
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
Option B is correct because 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.
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.
- ✗
Compilation fails
Why it's wrong here
Code compiles fine.
- ✓
3
Why this is correct
Correct, only unique elements counted.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
4
Why it's wrong here
Incorrect; duplicates are ignored.
- ✗
2
Why it's wrong here
Incorrect; there are three unique elements.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Detailed technical explanation
How to think about this question
HashSet is backed by a HashMap, where each element is stored as a key with a constant dummy value. When add() is called, it internally calls put() on the map, which uses the element's hashCode() to determine the bucket and equals() to check for duplicates; if a duplicate is found, the old value is replaced but the set size remains unchanged. This behavior is critical in scenarios like deduplicating user IDs or session tokens where uniqueness must be enforced.
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.
- →
Working with Arrays and Collections — study guide chapter
Learn the concepts, then practise the questions
- →
Working with Arrays and Collections practice questions
Targeted practice on this topic area only
- →
All 1Z0-829 questions
509 questions across all exam domains
- →
Oracle Certified Professional Java SE 17 Developer 1Z0-829 study guide
Full concept coverage aligned to exam objectives
- →
1Z0-829 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related 1Z0-829 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Handling Date, Time, Text, Numeric and Boolean Values practice questions
Practise 1Z0-829 questions linked to Handling Date, Time, Text, Numeric and Boolean Values.
Controlling Program Flow practice questions
Practise 1Z0-829 questions linked to Controlling Program Flow.
Utilizing Java Object-Oriented Approach practice questions
Practise 1Z0-829 questions linked to Utilizing Java Object-Oriented Approach.
Handling Exceptions practice questions
Practise 1Z0-829 questions linked to Handling Exceptions.
Working with Arrays and Collections practice questions
Practise 1Z0-829 questions linked to Working with Arrays and Collections.
Working with Streams and Lambda Expressions practice questions
Practise 1Z0-829 questions linked to Working with Streams and Lambda Expressions.
Java Platform Overview and Packaging practice questions
Practise 1Z0-829 questions linked to Java Platform Overview and Packaging.
Java I/O API and Securing Applications practice questions
Practise 1Z0-829 questions linked to Java I/O API and Securing Applications.
1Z0-829 fundamentals practice questions
Practise 1Z0-829 questions linked to 1Z0-829 fundamentals.
1Z0-829 scenario practice questions
Practise 1Z0-829 questions linked to 1Z0-829 scenario.
1Z0-829 troubleshooting practice questions
Practise 1Z0-829 questions linked to 1Z0-829 troubleshooting.
Practice this exam
Start a free 1Z0-829 practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
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: 3 — Option B is correct because 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.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Keep practising
More 1Z0-829 practice questions
- A financial application uses Java SE 17 with a custom date format. The requirement is to parse strings like "2023-12-31T…
- Which TWO statements about the switch statement in Java are correct?
- Which THREE statements are true about the java.util.Collection and java.util.stream.Stream APIs? (Choose three.)
- Which TWO of the following are checked exceptions in Java?
- A developer is implementing a custom sort for a list of Employee objects. The Employee class has fields: String name, in…
- What is the result of executing the code in the exhibit?
Last reviewed: Jun 11, 2026
This 1Z0-829 practice question is part of Courseiva's free Oracle certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 1Z0-829 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.