Quick Answer
The correct answer is encapsulation, as making all fields public directly violates this core object-oriented principle. Encapsulation requires that an object’s internal state be hidden from external access, with data only modifiable through controlled methods like getters and setters. When fields are declared public in Java, any class can read or modify them without restriction, breaking data integrity and the ability to enforce invariants such as validation or consistency checks. On the Oracle Java Foundations 1Z0-811 exam, this concept often appears in questions about design principles or class design, testing your understanding of why private fields are preferred. A common trap is confusing encapsulation with abstraction or inheritance, but remember: encapsulation is about hiding data, not just hiding implementation. For a quick memory tip, think of a capsule—if the capsule is open (public fields), the contents are exposed; encapsulation keeps the capsule sealed, protecting what’s inside.
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.
Which design principle is violated by making all fields public in a class?
Inheritance
Why wrong: Inheritance is about code reuse; public fields don't directly break it.
Abstraction
Why wrong: Abstraction hides implementation details; public fields expose them but abstraction is broader.
Encapsulation
Encapsulation hides internal data; public fields expose it.
Polymorphism
Why wrong: Polymorphism relates to method behavior, not 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
Making all fields public violates the principle of encapsulation, which requires that an object's internal state be hidden from external access and only modifiable through controlled methods (getters/setters). In Java, public fields allow any class to directly read or modify the field, breaking data integrity and the ability to enforce invariants. Encapsulation is a core OOP concept that protects the internal representation of an object.
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 is about code reuse; public fields don't directly break it.
Abstraction
Why it's wrong here
Abstraction hides implementation details; public fields expose them but abstraction is broader.
Encapsulation
Why this is correct
Encapsulation hides internal data; public fields expose it.
Related concept
Read the scenario before looking for a memorised answer.
Polymorphism
Why it's wrong here
Polymorphism relates to method behavior, not field access.
Common exam traps
Oracle often tests the distinction between OOP principles by presenting a scenario that seems to involve inheritance or abstraction, but the core violation is always about data hiding and controlled access—candidates mistakenly choose 'abstraction' because they confuse hiding implementation details with hiding data fields.
Detailed technical explanation
Encapsulation in Java is enforced by access modifiers (private, protected, public) and the use of getter/setter methods to control access. Under the hood, the JVM does not enforce encapsulation at the bytecode level—it is a compile-time and design-time constraint. A real-world scenario: a BankAccount class with a public balance field allows any code to set it to a negative value, whereas a private field with a setter can validate that withdrawals do not exceed the balance, preserving business rules.
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
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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 — Making all fields public violates the principle of encapsulation, which requires that an object's internal state be hidden from external access and only modifiable through controlled methods (getters/setters). In Java, public fields allow any class to directly read or modify the field, breaking data integrity and the ability to enforce invariants. Encapsulation is a core OOP concept that protects the internal representation of an object.
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 30, 2026
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