Quick Answer
The correct answer is encapsulation, because it enforces data hiding by making fields private and controlling access through public methods. In the BankAccount example, encapsulation would have allowed the developer to add validation logic inside a setter method for the balance field, preventing negative values from being assigned. This question tests your understanding of how encapsulation in Java protects object integrity through private fields and controlled access, a core concept on the Oracle Java Foundations 1Z0-811 exam. A common trap is confusing encapsulation with abstraction—remember that abstraction hides complexity, while encapsulation hides data and adds validation. For the exam, think of encapsulation as your code’s bouncer: it checks every value before letting it into the private club. Memory tip: “Private fields, public methods—validate before you let it in.”
This 1Z0-811 practice question tests your understanding of object-oriented programming. 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 junior developer created a class 'BankAccount' with public fields for balance and account number. After deployment, users are able to set negative balances, causing issues. Which OOP principle should have been applied to prevent this?
Inheritance
Why wrong: Inheritance does not prevent public field access.
Encapsulation
Encapsulation allows controlled access through methods with validation.
Abstraction
Why wrong: Abstraction is about hiding implementation, not data validation.
Polymorphism
Why wrong: Polymorphism does not restrict direct field access.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Encapsulation
Option C is correct because encapsulation would make the balance field private and provide a setter method that validates the value. Option A is wrong because polymorphism deals with method behavior, not data hiding. Option B is wrong because inheritance is about reusing code, not securing data. Option D is wrong because abstraction is about hiding complexity, not validation.
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.
Inheritance
Why it's wrong here
Inheritance does not prevent public field access.
Encapsulation
Why this is correct
Encapsulation allows controlled access through methods with validation.
Related concept
Read the scenario before looking for a memorised answer.
Abstraction
Why it's wrong here
Abstraction is about hiding implementation, not data validation.
Polymorphism
Why it's wrong here
Polymorphism does not restrict direct field access.
Common exam traps
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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 1Z0-811 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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FAQ
Object-Oriented Programming — This question tests Object-Oriented Programming — Read the scenario before looking for a memorised answer..
The correct answer is: Encapsulation — Option C is correct because encapsulation would make the balance field private and provide a setter method that validates the value. Option A is wrong because polymorphism deals with method behavior, not data hiding. Option B is wrong because inheritance is about reusing code, not securing data. Option D is wrong because abstraction is about hiding complexity, not validation.
Identify which 1Z0-811 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 23, 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.
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