OOP MCQs - Encapsulation, Abstraction and Access Specifiers (Set 2)

Q1. Which definition best describes encapsulation?

a) Bundling data with the methods that operate on it in one unit and restricting direct outside access to that data

b) Deriving a new class from an existing class to reuse its code

c) Allowing one interface to be used for different underlying forms

d) Splitting a program into separately compiled files

Q2. Which statement correctly distinguishes abstraction from encapsulation?

a) Abstraction is achieved only with private fields, while encapsulation needs interfaces

b) They are identical concepts; the terms are interchangeable

c) Abstraction exposes only the essential behaviour of an entity, while encapsulation hides how its state is stored and protects that state

d) Encapsulation applies only to functions, while abstraction applies only to variables

Q3. In C++, what is the default access level of members declared without an access specifier?

a) public in a class and private in a struct

b) private in a class and public in a struct

c) protected in both class and struct

d) private in both class and struct

Q4. In Java, a field declared with no access modifier is accessible from:

a) Any class in any package

b) Only the declaring class

c) Subclasses in any package, but not other classes in the same package

d) Only classes in the same package

Q5. What is the result of compiling and running this Java program?

class Acc {
    private int bal;
    Acc(int b) { bal = b; }
    boolean richerThan(Acc o) { return bal > o.bal; }
}
public class Main {
    public static void main(String[] args) {
        System.out.print(new Acc(50).richerThan(new Acc(80)));
    }
}

a) Compilation error: bal has private access

b) true

c) false

d) IllegalAccessError at run time

Q6. What does this Java program print?

class Box {
    private int[] d = {1, 2, 3};
    int[] get() { return d; }
}
public class Main {
    public static void main(String[] args) {
        Box b = new Box();
        b.get()[0] = 9;
        System.out.print(b.get()[0]);
    }
}

a) 1

b) 9

c) Compilation error

d) ArrayIndexOutOfBoundsException

Q7. What is printed by this C++ program?

#include <iostream>
using namespace std;
class Base {
protected: int p = 1;
private:   int q = 2;
public:    int r = 3;
};
class D : private Base {
public:
    int sum() { return p + r; }
};
int main() { D d; cout << d.sum(); }

a) 6

b) 4

c) Compilation error: p is protected in Base

d) Compilation error: r becomes private

Q8. Under public inheritance in C++, a protected member of the base class becomes ___ in the derived class.

a) protected

b) public

c) private

d) inaccessible

Q9. Which ordering of Java access levels runs from most restrictive to least restrictive?

a) public, protected, default, private

b) private, protected, default, public

c) default, private, protected, public

d) private, default (package), protected, public

Q10. Which modifier is NOT allowed on a top-level (non-nested) Java class?

a) public

b) abstract

c) final

d) private

Q11. Why is a setter method usually preferred over making a field public?

a) Setters are always faster than direct field access

b) Public fields cannot be read by other classes

c) A setter can validate input and enforce the class invariants before changing the state

d) Setters make a class immutable

Q12. Which practice would break the immutability of a Java class?

a) Adding a public method that changes one of its fields after construction

b) Declaring the class final

c) Making all fields private and final

d) Returning a copy of an internal mutable list from a getter

Q13. Which member functions of D compile?

class B { protected: int v = 1; };
class D : public B {
public:
    int f(B& other) { return other.v; }
    int g(D& other) { return other.v; }
};

a) Both f and g

b) Only g

c) Only f

d) Neither f nor g

Q14. A class stores a private List of orders. Which getter design best preserves encapsulation?

a) Return the internal list reference directly

b) Make the list public and remove the getter

c) Return an unmodifiable view or a copy of the list

d) Return the list cast to Object

Q15. Which language features are mainly used to achieve abstraction in object oriented design?

a) Global variables and macros

b) Abstract classes and interfaces that declare what operations exist without fixing their implementation

c) Inline functions and templates only

d) Pointer arithmetic and casting

Q16. Class Account in package bank declares a protected method audit(). A class Report in package util, which does NOT extend Account, calls acc.audit(). What happens?

a) It compiles because protected is the same as public outside the package

b) It compiles but throws an exception at run time

c) It compiles only if Report is in the same module

d) Compilation error, because protected access outside the package is granted only to subclasses

Q17. According to the information-hiding principle introduced by David Parnas, what should each module hide?

a) Design decisions that are likely to change, behind a stable interface

b) Its public interface, so other modules cannot call it

c) All of its data, including constants needed by callers

d) Its documentation from other developers

Q18. What is printed by this C++ program?

#include <iostream>
using namespace std;
class Cache {
    mutable int hits = 0;
    int v = 7;
public:
    int get() const { ++hits; return v; }
    int count() const { return hits; }
};
int main() {
    const Cache c;
    c.get(); c.get();
    cout << c.count();
}

a) 2

b) 0

c) 7

d) Compilation error: cannot modify a member in a const function