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Object Oriented Programming · Question Set
Abstraction & Encapsulation interview questions for placements and exams.
Questions
12
Included in this set
Subject
Object Oriented Programming
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Difficulty
Mixed
Level of this set
Go through each question and its explanation. Use this set as a focused practice pack for Object Oriented Programming.
Abstraction deals with exposing only essential features (the ‘what’), while encapsulation deals with hiding internal workings and grouping data and methods (the ‘how’) into a unit.
For complete preparation, combine this set with full subject-wise practice for Object Oriented Programming. You can also explore other subjects and sets from the links below.
Using the private modifier restricts a field or method to the defining class only. External classes must use public or protected methods (getters/setters) to interact, which enforces encapsulation.
An interface declares what methods a class must provide while hiding how they are implemented. This is a classic abstraction mechanism, focusing on behaviour rather than implementation.
By hiding internal state and exposing controlled access, encapsulation ensures the object’s data remains valid, prevents unauthorized changes, and reduces bugs caused by misuse of internal fields.
Abstract classes define interfaces or partial implementations. They require subclasses to provide concrete implementations and cannot be instantiated themselves, enforcing abstraction.
Encapsulation helps build modules by isolating internals behind exposed interfaces. This improves maintainability, readability, and reduces coupling between modules.
Abstraction allows developers to focus on high-level design rather than implementation details. By exposing only relevant behaviour, it simplifies usage and hides complexity. This leads to improved maintainability, scalability and easier evolution of systems. For instance in a banking application you might expose operations like deposit() and withdraw(), while hiding how interest calculation or ledger maintenance is implemented.
Imagine a `Vehicle` interface with method `startEngine()`. The `Car` class implements `Vehicle` and hides its internal `engine` object and wiring inside `Car`. Users call `car.startEngine()` (abstraction) without knowing internal details. Internally, `engine` field is private and only exposed via methods (encapsulation). This shows abstraction at interface level and encapsulation at implementation level. Understanding this distinction is valuable for interviews.
Abstraction simplifies complex systems by providing a high-level interface and hiding lower-level implementation details. It helps designers focus on what an object does rather than how it does it.
Encapsulation is about bundling data and methods that operate on that data within a class and restricting direct access from outside. This protects internal state and promotes modular design.
Consider a `BankAccount` class that keeps `balance` private and provides `deposit()` and `withdraw()` methods with internal checks (such as non-negative amounts and sufficient funds). This design hides the actual data, prevents external direct modification, enforces rules, and centralises validation logic. This encapsulation simplifies maintenance because changes to validation or logging only happen inside the class, not across the system.
If a class exposes its internal data directly (e.g., public fields), it opens the door to invalid state, brittle code and tight coupling. Changes to internal representation ripple across clients. To mitigate this, use access modifiers, provide well-defined interfaces, favour immutability, validate inputs in setters and keep internal logic behind private or protected methods. Designing classes with clear separation of concerns and using API contracts helps maintain encapsulation and system robustness.