Quick Answer
The answer is [10]. This is correct because `list.remove(1)` calls the overloaded `remove(int index)` method, which removes the element at the specified index position—in this case, index 1 holds the value 20—rather than searching for and removing the Integer object with value 1. The key technical distinction is that Java’s `ArrayList remove(int index)` vs `remove(Object)` methods are differentiated by parameter type: when you pass a primitive `int`, the compiler selects the index-based overload, not the object-based one. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this is a classic trap designed to test your understanding of method overloading resolution with autoboxing, especially when dealing with `List<Integer>`. A common memory tip is to remember that primitives always prefer the index version: if you want to remove the value 1 from a list of integers, you must explicitly pass `Integer.valueOf(1)` or cast to `Object` to force the object overload.
This 1Z0-829 practice question tests your understanding of utilizing java object-oriented approach. 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 the following code snippet: `List<Integer> list = new ArrayList<>(); list.add(10); list.add(20); list.remove(1); System.out.println(list);` What is the output?
[10, 20]
Why wrong: No removal? remove(1) removes index 1.
[]
Why wrong: Only one element is removed, not both.
[20]
Why wrong: Element at index 0 is not removed.
[10]
Element at index 1 (20) is removed.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
[10]
The code creates an ArrayList, adds 10 at index 0 and 20 at index 1. Then `list.remove(1)` removes the element at index 1, which is 20. The list now contains only [10]. Option D is correct because `remove(int index)` removes the element at the specified position, not the value.
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.
[10, 20]
Why it's wrong here
No removal? remove(1) removes index 1.
[]
Why it's wrong here
Only one element is removed, not both.
[20]
Why it's wrong here
Element at index 0 is not removed.
[10]
Why this is correct
Element at index 1 (20) is removed.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often confuse `remove(int index)` with `remove(Object o)`, mistakenly thinking `remove(1)` removes the value 1 instead of the element at index 1, leading them to choose option C or A.
Detailed technical explanation
The `List.remove(int index)` method removes the element at the specified position, shifting any subsequent elements to the left. In Java, `ArrayList` uses an internal array; removal involves copying elements from index+1 to the end, which is O(n) time complexity. Overloaded `remove(Object o)` removes the first occurrence of the specified value, which can cause confusion if a candidate misinterprets the parameter as a value rather than an index.
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
Utilizing Java Object-Oriented Approach — This question tests Utilizing Java Object-Oriented Approach — Read the scenario before looking for a memorised answer..
The correct answer is: [10] — The code creates an ArrayList, adds 10 at index 0 and 20 at index 1. Then `list.remove(1)` removes the element at index 1, which is 20. The list now contains only [10]. Option D is correct because `remove(int index)` removes the element at the specified position, not the value.
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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