Question 1

What is OOPs?

Accepted Answer

OOPs (Object-Oriented Programming System) is a programming paradigm that organizes software design around data, or 'objects', rather than functions or logic. An object represents a real-world entity that bundles data (attributes) and behavior (methods) together into a cohesive, reusable unit. Unlike procedural programming, which focuses on writing sequential functions to operate on data, OOPs focuses on creating objects that interact with one another. Each object is an instance of a class, which serves as its blueprint.

Question 2

What are the basic concepts of OOPs?

Accepted Answer

The four fundamental pillars of Object-Oriented Programming are Abstraction, Encapsulation, Inheritance, and Polymorphism. These four pillars work together to provide structure and stability to software designs: 
1. **Abstraction**: Hides complex internal execution details and displays only essential functionality.
2. **Encapsulation**: Bundles data and methods together inside a class and restricts direct access to protect internal state.
3. **Inheritance**: Allows a new class to acquire the properties and behaviors of an existing class, promoting reuse.
4. **Polymorphism**: Enables a single interface, method, or symbol to represent different underlying forms/behaviors.

Question 3

What is a class?

Accepted Answer

A class is a logical blueprint, template, or user-defined data type that describes the properties (state) and behaviors (methods) that objects of its type will possess. It does not occupy memory space until an instance is created. Think of a Class as an architectural drawing of a house. The drawing defines the rooms, dimensions, and styling, but it has no physical presence. The physical houses built using that drawing represent the actual objects that occupy space on land (or RAM in the computer).

Question 4

What is an Object?

Accepted Answer

An object is a physical instance of a class that occupies memory space. Every object possesses its own unique state (values of attributes), behavior (methods it can execute), and identity (its memory address or reference). While a class defines the properties, each object has its own unique values for those properties. For example, if 'Car' is the class, 'myCar' with brand='Tesla' and fuelLevel=100 is an object, while 'yourCar' with brand='Ford' and fuelLevel=50 is a separate, independent object stored at a different memory location.

Question 5

What is Encapsulation?

Accepted Answer

Encapsulation is the practice of bundling data variables and the methods that operate on them inside a single unit (a class) while restricting direct access to the internal data. It is achieved using private variables coupled with public getter and setter methods. Encapsulation prevents external code from modifying an object's internal state in an invalid or unauthorized way. This creates a secure black box. Access levels like Public, Protected, Private, Internal, and Protected Internal determine the visibility of variables.

Question 6

What is Polymorphism?

Accepted Answer

Polymorphism (meaning 'many forms') is the ability of an object, method, or operator to exhibit different behaviors depending on the context. In OOPs, it is divided into two types: Compile-time Polymorphism (Method Overloading) and Runtime Polymorphism (Method Overriding). Polymorphism allows you to define one interface and have multiple implementations. At compile time, the compiler resolves overloaded methods based on parameters. At runtime, the virtual machine resolves overridden methods dynamically based on the actual object type executing the command.

Question 7

What is Inheritance?

Accepted Answer

Inheritance is the mechanism by which a new class (subclass/derived class) derives its structure and behavior (properties and methods) from an existing class (superclass/base class). It promotes code reusability and establishes an 'IS-A' relationship. Inheritance avoids duplicate code. For example, a base class 'Vehicle' can define 'speed' and 'startEngine()'. Subclasses like 'Car' and 'Motorcycle' inherit these automatically while adding their own specific properties like 'trunkCapacity' or 'hasSidecar'.

Question 8

What are manipulators?

Accepted Answer

Manipulators are specialized helper functions in C++ that are used in conjunction with stream insertion (<<) and extraction (>>) operators to format and modify the input/output formatting of stream objects. Manipulators alter the stream state. For instance, `std::endl` inserts a newline character and flushes the output stream, while `std::setw(int)` sets the field width for the next output operation.

Question 9

Explain the term constructor.

Accepted Answer

A constructor is a special member method of a class that is automatically invoked when an object of that class is created. Its primary purpose is to initialize the state (attributes) of the newly created object. Constructors set up initial values. Key rules for constructors: 
1. They must have the exact same name as the class.
2. They do not have any return type (not even `void`).
3. If a programmer does not write a constructor, the compiler automatically provides a default parameterless constructor.

Question 10

Define Destructor?

Accepted Answer

A destructor is a special member method of a class that is called automatically when an object goes out of scope or is explicitly deleted. Its primary purpose is to release occupied resources, such as closing file handles, database connections, or freeing allocated memory. Destructors are critical in unmanaged languages like C++ to prevent memory leaks. The destructor shares the same name as the class but is prefixed with a tilde symbol (`~`). It cannot accept parameters and cannot return any value.

Question 11

What is an Inline function?

Accepted Answer

An inline function is a optimization technique where the compiler replaces the function call command with the actual, complete body code of the function during compilation, eliminating the runtime overhead of a standard function call. In C++, defining a function with the `inline` keyword is a request to the compiler. For small, frequently called helper functions, this eliminates the CPU cost of pushing arguments onto the stack and jumping to memory addresses. However, the compiler can ignore the request if the function is complex, contains loops, or is recursive.

Question 12

What is a virtual function?

Accepted Answer

A virtual function is a member function in a base class that is declared with the 'virtual' keyword, indicating to the compiler that its implementation can be overridden in derived classes. It enables Runtime Polymorphism (Late Binding) using a virtual table (vtable). When you call a virtual function through a base class pointer or reference pointing to a child class object, the compiler does not resolve the call at compile time. Instead, it looks up the actual object's vtable at runtime to locate and execute the overridden child method.

Question 13

What is a friend function?

Accepted Answer

A friend function is a non-member function defined outside a class that is explicitly granted permission to access the private and protected members of that class. It is declared inside the class definition using the 'friend' keyword. Friend functions break access control walls. They are typically used for utility functions, global operator overloading, or bridging interactions between two separate classes without exposing private variables to the public interface.

Question 14

What is function overloading?

Accepted Answer

Function overloading is a compile-time polymorphism feature that allows a class to have multiple methods with the exact same name but with different parameter lists (different number of arguments, types of arguments, or order of arguments). The compiler distinguishes overloaded methods by their signature (number, type, and order of parameters). Note that overloading cannot be achieved by changing only the return type of the method; the parameters must differ.

Question 15

What is operator overloading?

Accepted Answer

Operator overloading is a feature in languages like C++ and C# that allows developers to redefine the default behavior of standard operators (+, -, *, ==, <<, etc.) when they are applied to user-defined class objects. Operator overloading makes custom class objects behave intuitively like native primitive variables. For example, you can overload the '+' operator for a 'ComplexNumber' class or a 'Matrix' class to add objects together cleanly.

OOPs Foundations Interview Prep Portal

What is OOPs?

What are the basic concepts of OOPs?

What is a class?

What is an Object?

What is Encapsulation?

What is Polymorphism?

What is Inheritance?

What are manipulators?

Explain the term constructor.

Define Destructor?

What is an Inline function?

What is a virtual function?

What is a friend function?

What is function overloading?

What is operator overloading?

What is an abstract class?

What is a ternary operator?

What is the use of finalize method?

What are the different types of arguments?

What is the super keyword?

What is method overriding?

What is an interface?

What is exception handling?

What are tokens?

What is the main difference between overloading and overriding?

What is the main difference between a class and an object?

What is an abstraction?

What are the access modifiers?

What are sealed modifiers?

How can we call the base method without creating an instance?

What is the difference between new and override?

What are the various types of constructors?

What is early and late Binding?

What is 'this' pointer?

What is the difference between structure and a class?

What is the default access modifier in a class?

What is a pure virtual function?

What are all the operators that cannot be overloaded?

What is dynamic or runtime polymorphism?

Do we require a parameter for constructors?

What is a copy constructor?

What does the keyword virtual represent in the method definition?

Whether static method can use non-static members?

What are a base class, subclass, and superclass?

What is static and dynamic Binding?

How many instances can be created for an abstract class?

Which keyword can be used for overloading?

What is the default access specifier in a class definition?

Which OOPs concept is used as a reuse mechanism?

Which OOPs concept exposes only the necessary information to the calling functions?

OOPs Foundations
Interview Prep Portal