Quick Answer
The answer is that a ConcurrentModificationException is thrown. This occurs because the for-each loop in Java internally uses an Iterator to traverse the ArrayList, and calling list.remove() directly during iteration structurally modifies the list without updating the iterator’s internal state. The iterator’s fail-fast mechanism detects this mismatch via a modCount check and immediately throws the exception. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this question tests your understanding of fail-fast iterators and the distinction between using the collection’s own remove() versus the iterator’s remove() method—a classic trap where candidates mistakenly think the loop will skip elements or complete silently. Remember: when iterating an ArrayList with a for-each loop, never modify the list directly; always use the iterator’s own remove() if removal is needed. A useful memory tip: “For-each is read-only unless you use the iterator’s own remove.”
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.
Examine the code: List<String> list = new ArrayList<>(); list.add("A"); list.add("B"); for (String s : list) { list.remove(s); } What is the outcome?
A ConcurrentModificationException is thrown
Modifying list during iteration with for-each throws exception.
The loop completes successfully and list becomes empty
Why wrong: Exception prevents completion.
An IllegalStateException is thrown
Why wrong: ConcurrentModificationException is thrown.
The loop completes successfully and list contains [B]
Why wrong: Exception thrown.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
A ConcurrentModificationException is thrown
The for-each loop internally uses an Iterator to traverse the list. When the list is structurally modified (via `list.remove()`) during iteration without using the iterator's own `remove()` method, the iterator detects a concurrent modification and throws a `ConcurrentModificationException`. This is a fail-fast behavior of the `ArrayList` iterator.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
A ConcurrentModificationException is thrown
Why this is correct
Modifying list during iteration with for-each throws exception.
Related concept
Read the scenario before looking for a memorised answer.
The loop completes successfully and list becomes empty
Why it's wrong here
Exception prevents completion.
An IllegalStateException is thrown
Why it's wrong here
ConcurrentModificationException is thrown.
The loop completes successfully and list contains [B]
Why it's wrong here
Exception thrown.
Common exam traps
The trap here is that candidates often assume the for-each loop will safely remove elements one by one, not realizing that the implicit iterator throws an exception on structural modification.
Detailed technical explanation
Under the hood, `ArrayList` maintains a `modCount` field that tracks structural modifications. The iterator checks this count against its own `expectedModCount` on each `next()` call; if they differ, it throws `ConcurrentModificationException`. In this code, the first iteration removes "A", incrementing `modCount`, and the iterator's `next()` call on the second iteration detects the mismatch. This fail-fast mechanism is designed to catch bugs early in single-threaded code, but in multi-threaded scenarios it does not guarantee thread safety.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise 1Z0-829 questions linked to Handling Date, Time, Text, Numeric and Boolean Values.
Practise 1Z0-829 questions linked to Controlling Program Flow.
Practise 1Z0-829 questions linked to Utilizing Java Object-Oriented Approach.
Practise 1Z0-829 questions linked to Handling Exceptions.
Practise 1Z0-829 questions linked to Working with Arrays and Collections.
Practise 1Z0-829 questions linked to Working with Streams and Lambda Expressions.
Practise 1Z0-829 questions linked to Java Platform Overview and Packaging.
Practise 1Z0-829 questions linked to Java I/O API and Securing Applications.
Practise 1Z0-829 questions linked to 1Z0-829 fundamentals.
Practise 1Z0-829 questions linked to 1Z0-829 scenario.
Practise 1Z0-829 questions linked to 1Z0-829 troubleshooting.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Working with Arrays and Collections — This question tests Working with Arrays and Collections — Read the scenario before looking for a memorised answer..
The correct answer is: A ConcurrentModificationException is thrown — The for-each loop internally uses an Iterator to traverse the list. When the list is structurally modified (via `list.remove()`) during iteration without using the iterator's own `remove()` method, the iterator detects a concurrent modification and throws a `ConcurrentModificationException`. This is a fail-fast behavior of the `ArrayList` iterator.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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 25, 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.