Question 1hardmultiple choice
Full question →- A
20
Why wrong: This is the last element, not first.
- B
15
Why wrong: Not the first element.
- C
5
Correct; first() returns the least element in reversed order.
- D
10
Why wrong: Not the first element.
Question 247 of 509
Quick Answer
The answer is 5. This is correct because TreeSet’s first() method returns the smallest element according to the comparator provided at construction, not the natural order. When you use Comparator.reverseOrder(), the set stores elements in descending order (20, 15, 10, 5), so the “first” element in that reversed ordering is actually the smallest value, which is 5. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this question tests your understanding of how TreeSet first() with reverse comparator behaves—a common trap is assuming first() always returns the lowest natural number. Instead, remember that first() always returns the element that would come first in the set’s current sorted order, which is determined by the comparator. A useful memory tip: “Reverse the order, reverse your intuition—first becomes last in natural terms.”
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: TreeSet<Integer> ts = new TreeSet<>(Comparator.reverseOrder()); ts.add(10); ts.add(5); ts.add(20); ts.add(15); System.out.println(ts.first()); What is the result?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"first"Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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
✓
5
Option C is correct because `TreeSet` with `Comparator.reverseOrder()` sorts elements in descending order (20, 15, 10, 5). The `first()` method returns the smallest element according to the comparator, which in descending order is the last element in the natural order, i.e., 5.
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.
- ✗
20
Why it's wrong here
This is the last element, not first.
- ✗
15
Why it's wrong here
Not the first element.
- ✓
5
Why this is correct
Correct; first() returns the least element in reversed order.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
10
Why it's wrong here
Not the first element.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume `first()` returns the first element added or the largest element in a reversed set, rather than understanding it always returns the smallest element according to the set's comparator.
Detailed technical explanation
How to think about this question
Under the hood, `TreeSet` uses a `TreeMap` with the provided comparator to maintain a red-black tree structure. The `first()` method retrieves the minimum key from the tree, which is determined by traversing leftmost nodes according to the comparator's ordering. In descending order, the 'minimum' is the element that would be last in natural order, so `first()` returns 5. This behavior is crucial when using custom comparators that invert natural ordering.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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: 5 — Option C is correct because `TreeSet` with `Comparator.reverseOrder()` sorts elements in descending order (20, 15, 10, 5). The `first()` method returns the smallest element according to the comparator, which in descending order is the last element in the natural order, i.e., 5.
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.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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 →
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.