OOP MCQs - Classes, Objects, Constructors and Destructors (Set 1)

Q1. Which statement best describes the relationship between a class and an object?

a) A class is a blueprint that defines state and behaviour; an object is a concrete instance of it with its own state

b) An object is a template from which many classes are created at run time

c) A class and an object are the same thing, named differently in different languages

d) A class occupies memory for its data members, while an object only stores method addresses

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

#include <iostream>
using namespace std;
struct T {
    int id;
    T(int i) : id(i) { cout << "C" << id; }
    ~T() { cout << "D" << id; }
};
int main() {
    T a(1);
    { T b(2); }
    T c(3);
}

a) C1C2C3D3D2D1

b) C1C2D2C3D3D1

c) C1C2D2C3D1D3

d) C1C2C3D1D2D3

Q3. Why must the parameter of a C++ copy constructor be a reference (usually const T&) rather than a value?

a) Because references are faster than pointers for all types

b) Because the compiler cannot copy objects that contain private members

c) Because passing by value would itself need a copy constructor call, leading to infinite recursion

d) Because a value parameter would make the constructor static

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

#include <iostream>
using namespace std;
struct P {
    P() { cout << "d"; }
    P(const P&) { cout << "c"; }
};
void f(P x) {}
int main() {
    P a;
    P b = a;
    f(b);
}

a) dc

b) ddc

c) dcc

d) dccc

Q5. When does a C++ compiler implicitly declare a default (no-argument) constructor for a class?

a) Always, even if the programmer writes other constructors

b) Only when the class has at least one virtual function

c) Only when every data member is public

d) Only when the programmer has not declared any constructor at all

Q6. In C++, which of the following situations does NOT invoke the copy constructor?

a) Initialising a new object from an existing one: Point q = p;

b) Passing an object by value to a function

c) Direct-initialising a new object: Point q(p);

d) Assigning one already-existing object to another: q = p;

Q7. A C++ class holds a raw pointer to a heap buffer and frees it in its destructor, but relies on the compiler-generated copy constructor. What is the most likely problem after copying an object?

a) Both objects point to the same buffer, so the buffer is deleted twice when they are destroyed

b) The copy gets a fresh buffer with garbage values

c) The program will not compile because pointers cannot be copied

d) The original object's pointer is set to nullptr automatically

Q8. What is printed by this C++ program?

#include <iostream>
using namespace std;
struct X {
    static int n;
    X() { ++n; }
    ~X() { --n; }
};
int X::n = 0;
int main() {
    X a[3];
    X* p = new X;
    cout << X::n;
    delete p;
    cout << X::n;
}

a) 43

b) 44

c) 33

d) 40

Q9. Which statement about C++ destructors is correct?

a) A class may overload its destructor with different parameter lists

b) A class has exactly one destructor, and it takes no arguments and has no return type

c) A destructor must always be called explicitly by the programmer

d) A destructor runs before the constructor when an object is created

Q10. What is printed when this Java program runs?

class A {
    A() { System.out.print("A"); }
    { System.out.print("I"); }
    static { System.out.print("S"); }
}
public class Main {
    public static void main(String[] args) {
        new A();
        new A();
    }
}

a) SAISAI

b) SIASIA

c) SIAIA

d) ISAIA

Q11. What is printed by this C++ program?

#include <iostream>
using namespace std;
struct M {
    int v;
    M(int a = 7) : v(a) { cout << "M" << v; }
};
int main() {
    M x;
    M y(3);
    M z = 5;
    M w();
}

a) M7M3M5M7

b) M7M3M5

c) M7M3

d) Compilation error

Q12. A C++ class Date has only the constructor Date(int d = 1, int m = 1). Which statement is correct?

a) Date cannot be created without passing arguments

b) This constructor also acts as the default constructor of Date

c) The compiler additionally generates a separate no-argument constructor

d) The constructor must be declared explicit to compile

Q13. In Java, when does an object become eligible for garbage collection?

a) As soon as the method that created it returns, regardless of references

b) Only when System.gc() is called on it explicitly

c) When it is no longer reachable through any chain of references from live threads or static fields

d) When its finalize() method has been called by the programmer

Q14. In C++, data members of a class are initialised in which order?

a) The order they appear in the constructor's member initialiser list

b) Alphabetical order of member names

c) Reverse order of declaration

d) The order in which they are declared in the class, regardless of the initialiser list order

Q15. Java has no destructors. Which mechanism is the recommended way to release a resource such as a file handle deterministically?

a) A try-with-resources statement on an object implementing AutoCloseable

b) Overriding finalize() in the class

c) Setting the reference to null and calling System.gc()

d) Declaring the field as transient

Q16. What is the typical signature and purpose of a C++11 move constructor for class Buf?

a) Buf(const Buf&) - duplicates every heap resource of the source

b) Buf(Buf*) - copies only the pointer of the source object

c) Buf(Buf&&) - takes over the resources of a temporary or expiring object, leaving it in a valid empty state

d) Buf(const Buf&&) - makes a deep copy that cannot be modified

Q17. What is a common reason for declaring all constructors of a class private?

a) To make the class abstract so it must be inherited

b) To stop outside code creating instances directly, for example in utility classes or classes that create objects only through static factory methods

c) To allow the class to be instantiated without memory allocation

d) To force the compiler to generate a public copy constructor

Q18. What is printed by this Java program?

class Pt {
    int x;
    Pt(int x) { this.x = x; }
}
public class Main {
    public static void main(String[] args) {
        Pt p = new Pt(4);
        Pt q = p;
        q.x = 9;
        Pt r = new Pt(9);
        System.out.print(p.x + " " + (q == p) + " " + (r == p));
    }
}

a) 4 true false

b) 9 true true

c) 4 false false

d) 9 true false