The answer is [A, D, C]. This output occurs because the comparator compares strings solely by their length, and since "A", "D", and "C" all have a length of 1, the comparator returns 0 for every pairwise comparison. When a comparator returns 0 for equal elements, a stable sort with comparator ensures that the original insertion order is preserved, so the list remains unchanged from its initial state. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this tests your understanding of the `List.sort()` method combined with a `Comparator` that produces ties, and it is a common trap to assume that equal-length strings will be reordered alphabetically. The key insight is that stability only matters when the comparator considers elements equal, and here all lengths are equal, so no swapping occurs. Memory tip: when lengths match, the sort takes a nap—original order stays in your lap.
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.
Exhibit
Refer to the exhibit.
```java
import java.util.*;
public class Test {
public static void main(String[] args) {
List<String> list = new ArrayList<>();
list.add("A");
list.add("B");
list.add("C");
list.remove(1);
list.add(1, "D");
System.out.println(list);
}
}
```
Refer to the exhibit.
```java
import java.util.*;
public class Test {
public static void main(String[] args) {
List<String> list = new ArrayList<>();
list.add("A");
list.add("B");
list.add("C");
list.remove(1);
list.add(1, "D");
System.out.println(list);
}
}
```
A
[A, D, C]
Correct sequence after operations.
B
[A, C, D]
Why wrong: This would happen if add were at end, not at index 1.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
[A, D, C]
The code sorts the list using a comparator that compares strings by their length. Since "A" has length 1, "D" has length 1, and "C" has length 1, all three strings have the same length, so the comparator returns 0 for all comparisons, meaning the sort is stable and the original order [A, D, C] is preserved.
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.
✓
[A, D, C]
Why this is correct
Correct sequence after operations.
Related concept
Read the scenario before looking for a memorised answer.
✗
[A, C, D]
Why it's wrong here
This would happen if add were at end, not at index 1.
✗
[A, B, C]
Why it's wrong here
No removal or addition performed?
✗
[A, D, B]
Why it's wrong here
B was removed, so it cannot appear.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a comparator based on length will always reorder elements, but when all lengths are equal, the sort is stable and the original order is preserved, leading to the incorrect expectation of alphabetical or other ordering.
Detailed technical explanation
How to think about this question
The `Comparator.comparingInt(String::length)` creates a comparator that uses `Integer.compare` on the lengths. When all lengths are equal, the sort is stable (as per the Java specification for `List.sort`), meaning the relative order of equal elements is unchanged. This is a common pitfall: developers often forget that a comparator returning 0 does not reorder elements, and the original insertion order is retained.
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: [A, D, C] — The code sorts the list using a comparator that compares strings by their length. Since "A" has length 1, "D" has length 1, and "C" has length 1, all three strings have the same length, so the comparator returns 0 for all comparisons, meaning the sort is stable and the original order [A, D, C] is preserved.
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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