OOP MCQs - Inheritance and Constructor Call Order (Set 3)

Q1. Public inheritance should be used to model which relationship between classes?

a) IS-A, where the derived class is a specialised kind of the base

b) HAS-A, where one class contains another

c) USES-A, where one class calls another temporarily

d) PART-OF, where the lifetime of one depends on the other

Q2. What is printed by this C++ program?

#include <iostream>
using namespace std;
struct A { A() { cout << "A"; } ~A() { cout << "~A"; } };
struct B : A { B() { cout << "B"; } ~B() { cout << "~B"; } };
struct C : B { C() { cout << "C"; } ~C() { cout << "~C"; } };
int main() { C c; }

a) ABC~A~B~C

b) CBA~C~B~A

c) ABC~C~B~A

d) ABC~C

Q3. What is printed by this C++ program?

#include <iostream>
using namespace std;
struct X { X() { cout << "X"; } };
struct Y { Y() { cout << "Y"; } };
struct Z : Y, X {
    Z() : X(), Y() { cout << "Z"; }
};
int main() { Z z; }

a) XYZ

b) YXZ

c) ZYX

d) Compilation error: initialiser list order mismatch

Q4. What is printed by this C++ program?

#include <iostream>
using namespace std;
struct A { A() { cout << "A"; } };
struct B : virtual A { B() { cout << "B"; } };
struct C : virtual A { C() { cout << "C"; } };
struct D : B, C { D() { cout << "D"; } };
int main() { D d; }

a) ABACD

b) ABCD

c) BCAD

d) ABCDA

Q5. What exactly is the diamond problem in multiple inheritance?

a) A derived class cannot have more than two base classes

b) Constructors of a class are called in an unpredictable order

c) A base class cannot be inherited privately

d) A class inherits from two classes that share a common base, so it may get two copies of that base and ambiguous member lookups

Q6. Which Java declaration will NOT compile?

a) class C extends A, B { }

b) class C extends A implements I, J { }

c) interface K extends I, J { }

d) class C implements I, J { }

Q7. A design has class Vehicle, classes Car and Truck derived from it, and class PickUp derived from both Car and Truck. What kind of inheritance is this as a whole?

a) Single

b) Multilevel

c) Hybrid

d) Hierarchical only

Q8. Classes Circle, Square and Triangle all derive directly from a single class Shape, and none derives from another. This is an example of:

a) Multiple inheritance

b) Multilevel inheritance

c) Hybrid inheritance

d) Hierarchical inheritance

Q9. What does this Java program print?

class G { G() { System.out.print("G"); } }
class H extends G {
    H() { this(1); System.out.print("H"); }
    H(int x) { System.out.print("h"); }
}
public class Main {
    public static void main(String[] args) { new H(); }
}

a) HhG

b) hGH

c) GHhH

d) GhH

Q10. What does this Java program print?

class P { String n = "P"; String who() { return "P"; } }
class Q extends P { String n = "Q"; String who() { return "Q"; } }
public class Main {
    public static void main(String[] args) {
        P r = new Q();
        System.out.print(r.n + r.who() + ((Q) r).n);
    }
}

a) PQQ

b) QQQ

c) PPQ

d) QPQ

Q11. By default, which of the following is NOT inherited by a derived class in C++?

a) Public member functions of the base

b) Protected data members of the base

c) Friendship granted by the base class

d) Static data members of the base

Q12. In a C++ diamond (A as the base of B and C; D derives from B and C) using ordinary non-virtual inheritance, how many A subobjects does a D object contain?

a) 1

b) 2

c) 3

d) 0

Q13. What is the main reason behind the guideline 'favour composition over inheritance'?

a) Inheritance couples the subclass tightly to the base class implementation, so changes to the base can break subclasses

b) Composition is always faster at run time

c) Inheritance is not supported by most modern languages

d) Composition removes the need for interfaces

Q14. Where must an explicit super(...) call appear inside a Java constructor?

a) Anywhere, as long as it is called exactly once

b) As the last statement of the constructor

c) Inside a static initialiser block

d) As the first statement of the constructor body

Q15. What is the result of compiling and running this C++ program?

#include <iostream>
using namespace std;
struct Base { Base(int x) { cout << x; } };
struct Derived : Base {
    Derived() { cout << "D"; }
};
int main() { Derived d; }

a) D

b) 0D

c) Compilation error

d) A garbage value followed by D

Q16. Classes B and C both define a public function show(), and D inherits publicly from both. For a D object d, how can C++ code call B's version unambiguously?

a) d.B::show();

b) d.show(B);

c) d->B.show();

d) B::d.show();

Q17. Which Java keyword, applied to a class, prevents any class from extending it?

a) static

b) abstract

c) private

d) final

Q18. Class D publicly inherits from class B in C++. Which conversion happens implicitly without a cast?

a) B* to D*

b) D* to B*

c) B object to D object

d) void* to D*