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.
A developer needs to iterate over an ArrayList of integers and remove all elements that are less than 10. Which approach is best to avoid ConcurrentModificationException?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use list.removeIf() with a lambda expression.
Option D is correct because `list.removeIf()` is a built-in method introduced in Java 8 that safely removes elements from a collection based on a predicate, handling all iteration and modification internally without throwing ConcurrentModificationException. It uses an internal iterator that properly coordinates structural modifications, making it the most concise and reliable approach for this task.
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.
✗
Use a for loop with index and list.remove(index) decrementing index.
Why it's wrong here
Works but error-prone; requires careful index handling.
✗
Use an Iterator with iterator.remove().
Why it's wrong here
Works but is not the best approach; removeIf is more concise.
✗
Use a for-each loop with list.remove().
Why it's wrong here
Using for-each with list.remove() throws ConcurrentModificationException.
✓
Use list.removeIf() with a lambda expression.
Why this is correct
removeIf is the cleanest and safest way; it uses an internal iterator and avoids ConcurrentModificationException.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose the Iterator approach (Option B) because they know it avoids ConcurrentModificationException, but they overlook that `removeIf()` is the more modern, concise, and recommended method for such bulk removal operations in Java.
Detailed technical explanation
How to think about this question
Under the hood, `ArrayList.removeIf()` uses a `BitSet` to mark elements for removal and then performs a single bulk shift of the remaining elements, making it O(n) and efficient. This contrasts with `Iterator.remove()`, which removes one element at a time and can cause O(n^2) performance if many elements are removed due to repeated array shifting. In real-world scenarios like filtering large datasets, `removeIf()` is preferred for both safety and performance.
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 — 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: Use list.removeIf() with a lambda expression. — Option D is correct because `list.removeIf()` is a built-in method introduced in Java 8 that safely removes elements from a collection based on a predicate, handling all iteration and modification internally without throwing ConcurrentModificationException. It uses an internal iterator that properly coordinates structural modifications, making it the most concise and reliable approach for this task.
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: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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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