1Z0-811 Object-Oriented Programming Practice Question
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?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Encapsulation
Encapsulation involves making fields private and providing controlled access via methods. By encapsulating the balance field, a setter method can validate that the balance is not set to a negative value, preventing the issue. Option A (Inheritance) is about code reuse, not data hiding. Option C (Abstraction) is about hiding complexity, not enforcing validation. Option D (Polymorphism) is about methods behaving differently, not data protection.
Answer analysis
Option-by-option breakdown
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.
- ✗
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.
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