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 ArrayList<Integer> numbers = new ArrayList<>(List.of(1,2,3,4)); Which statement will insert element 10 at index 2?
numbers.add(10,2);
Why wrong: The add method expects index first, then element; this would attempt to add at index 10, causing IndexOutOfBoundsException.
numbers.add(2,10);
Inserts 10 at index 2, shifting subsequent elements to the right.
numbers.set(2,10);
Why wrong: set replaces the element at index 2, not insert.
numbers.insert(2,10);
Why wrong: No insert method exists in List or ArrayList.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
numbers.add(2,10);
Option B is correct because the `ArrayList.add(int index, E element)` method inserts the specified element at the given index, shifting existing elements to the right. Here, `numbers.add(2,10)` inserts 10 at index 2, resulting in the list [1,2,10,3,4].
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.
numbers.add(10,2);
Why it's wrong here
The add method expects index first, then element; this would attempt to add at index 10, causing IndexOutOfBoundsException.
numbers.add(2,10);
Why this is correct
Inserts 10 at index 2, shifting subsequent elements to the right.
Related concept
Read the scenario before looking for a memorised answer.
numbers.set(2,10);
Why it's wrong here
set replaces the element at index 2, not insert.
numbers.insert(2,10);
Why it's wrong here
No insert method exists in List or ArrayList.
Common exam traps
The trap here is that candidates often confuse the `add(index, element)` method with `set(index, element)`, mistakenly thinking both insert, or they reverse the argument order, expecting `add(element, index)` as in some other languages.
Detailed technical explanation
The `add(int index, E element)` method runs in O(n) time because it must shift all elements from the given index to the end of the list to make room. Under the hood, `ArrayList` uses an `Object[]` array; when inserting, it calls `System.arraycopy()` to shift elements, and if the internal array is full, it grows by 50% (1.5x) before insertion. This is distinct from `LinkedList`, where insertion at a known index is O(n) due to traversal, but actual node insertion is O(1).
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
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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: numbers.add(2,10); — Option B is correct because the `ArrayList.add(int index, E element)` method inserts the specified element at the given index, shifting existing elements to the right. Here, `numbers.add(2,10)` inserts 10 at index 2, resulting in the list [1,2,10,3,4].
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.
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Last reviewed: Jun 25, 2026
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