Quick Answer
The answer is HashMap<String, Integer> because it stores key-value pairs where each genre name (String) is a unique key mapped to its count (Integer), directly fulfilling the requirement of unique keys for genre counts. This data structure leverages hashing to achieve O(1) average-time complexity for lookups and updates, making it ideal for frequent access with rare modifications. On the Oracle Java Foundations 1Z0-811 exam, this question tests your understanding of when to choose a Map over a List or Set—a common trap is selecting an ArrayList and manually checking for duplicates, which is inefficient. Remember that HashMap enforces key uniqueness automatically via its hash-based implementation, while TreeMap would add sorting overhead you don’t need here. A simple memory tip: “Hash the key, map the value, keep it unique.”
This 1Z0-811 practice question tests your understanding of java basics and syntax. 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.
You are developing a Java application for a library management system. The system must track the number of books in each genre. You need to store genre names (String) and their counts (int). The data will be accessed frequently and modified rarely. Which Java data structure should you use to store this mapping efficiently, while ensuring that genre names are unique?
ArrayList<Book>
Why wrong: Not a mapping structure; duplicates allowed.
LinkedList<String>
Why wrong: No mapping, inefficient search.
HashSet<String>
Why wrong: Only keys, no count.
HashMap<String, Integer>
Maps unique genre to count.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
HashMap<String, Integer>
HashMap<String, Integer> is the correct choice because it stores key-value pairs, where each genre name (String) is a unique key mapped to its count (Integer). This provides O(1) average-time complexity for lookups and updates, which is ideal for frequent access and rare modifications. The HashMap ensures key uniqueness via its hash-based implementation, directly meeting the requirement of unique genre names.
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.
ArrayList<Book>
Why it's wrong here
Not a mapping structure; duplicates allowed.
LinkedList<String>
Why it's wrong here
No mapping, inefficient search.
HashSet<String>
Why it's wrong here
Only keys, no count.
HashMap<String, Integer>
Why this is correct
Maps unique genre to count.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Oracle often tests the distinction between collections that store single elements (like HashSet) versus those that store key-value pairs (like HashMap), leading candidates to choose HashSet when a mapping is required.
Detailed technical explanation
HashMap uses an array of buckets internally, where each bucket is a linked list or tree (since Java 8) to handle collisions via the hashCode() and equals() methods. The load factor (default 0.75) triggers rehashing when the map exceeds this threshold, ensuring performance remains near O(1) for get/put operations. In a library system with thousands of genres, this structure efficiently handles concurrent reads while maintaining uniqueness through the key's hash code.
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 1Z0-811 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
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Java Basics and Syntax — study guide chapter
Learn the concepts, then practise the questions
Java Basics and Syntax practice questions
Targeted practice on this topic area only
All 1Z0-811 questions
509 questions across all exam domains
Oracle Java Foundations 1Z0-811 study guide
Full concept coverage aligned to exam objectives
1Z0-811 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise 1Z0-811 questions linked to What is Java.
Practise 1Z0-811 questions linked to Java Basics and Syntax.
Practise 1Z0-811 questions linked to Primitives, Strings and Operators.
Practise 1Z0-811 questions linked to Control Flow and Loops.
Practise 1Z0-811 questions linked to Arrays and Methods.
Practise 1Z0-811 questions linked to Object-Oriented Programming.
Practise 1Z0-811 questions linked to Exception Handling and Development Tools.
Practise 1Z0-811 questions linked to 1Z0-811 fundamentals.
Practise 1Z0-811 questions linked to 1Z0-811 scenario.
Practise 1Z0-811 questions linked to 1Z0-811 troubleshooting.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Java Basics and Syntax — This question tests Java Basics and Syntax — Read the scenario before looking for a memorised answer..
The correct answer is: HashMap<String, Integer> — HashMap<String, Integer> is the correct choice because it stores key-value pairs, where each genre name (String) is a unique key mapped to its count (Integer). This provides O(1) average-time complexity for lookups and updates, which is ideal for frequent access and rare modifications. The HashMap ensures key uniqueness via its hash-based implementation, directly meeting the requirement of unique genre names.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jun 30, 2026
This 1Z0-811 practice question is part of Courseiva's free Oracle certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 1Z0-811 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.