1Z0-829 Working with Arrays and Collections Practice Question
This 1Z0-829 practice question tests your understanding of working with arrays and collections. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Exhibit
Refer to the exhibit.
```
List<String> list = new ArrayList<>(List.of("A", "B", "C"));
for (String s : list) {
if (s.equals("B")) {
list.remove(s);
}
}
System.out.println(list);
```
What is the result of executing the code in the exhibit?
Refer to the exhibit.
```
List<String> list = new ArrayList<>(List.of("A", "B", "C"));
for (String s : list) {
if (s.equals("B")) {
list.remove(s);
}
}
System.out.println(list);
```
A
The code compiles and runs without output.
Why wrong: Exception is thrown and printed.
B
[A, C]
Why wrong: Would be result if no exception, but exception is thrown.
C
ConcurrentModificationException is thrown.
Modification during enhanced for loop causes exception.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ConcurrentModificationException is thrown.
The code uses an ArrayList and iterates over it with an enhanced for-each loop while simultaneously removing an element via the list's remove() method. This structural modification directly from the list (not via the iterator's remove()) triggers a ConcurrentModificationException because the iterator's modCount check fails. The exception is thrown at the next iteration attempt after the removal.
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.
✗
The code compiles and runs without output.
Why it's wrong here
Exception is thrown and printed.
✗
[A, C]
Why it's wrong here
Would be result if no exception, but exception is thrown.
✓
ConcurrentModificationException is thrown.
Why this is correct
Modification during enhanced for loop causes exception.
Related concept
Read the scenario before looking for a memorised answer.
✗
[A, B]
Why it's wrong here
Incorrect removal.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think removing an element during iteration is safe if done via the list's remove() method, not realizing that the for-each loop's iterator detects the structural modification and throws ConcurrentModificationException.
Detailed technical explanation
How to think about this question
Under the hood, the enhanced for-each loop uses an iterator internally. The ArrayList's iterator maintains a modCount field that tracks structural modifications. When list.remove() is called, it increments the list's modCount but not the iterator's expectedModCount, causing a mismatch on the next hasNext() or next() call, which throws ConcurrentModificationException. This is a fail-fast behavior designed to detect concurrent modification bugs early. In real-world scenarios, this often occurs when developers mistakenly use list.remove() inside a for-each loop instead of using the iterator's remove() method or collecting removals for later processing.
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 — 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: ConcurrentModificationException is thrown. — The code uses an ArrayList and iterates over it with an enhanced for-each loop while simultaneously removing an element via the list's remove() method. This structural modification directly from the list (not via the iterator's remove()) triggers a ConcurrentModificationException because the iterator's modCount check fails. The exception is thrown at the next iteration attempt after the removal.
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.
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Question Discussion
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