OOPs Interview Questions and Answers

Object-Oriented Programming, commonly known as OOPs, is a programming paradigm that revolves around the concept of objects in a program. The main aim of OOPs is to provide a simpler and more efficient solution to real-world problems by implementing real-world entities such as inheritance, abstraction, polymorphism, etc. into programming.

OOPs, are widely used in many popular programming languages such as Java, Python, C++, etc. It offers many benefits, such as code reusability, easy maintenance, and scalability, which makes it a preferred choice for developing complex and large-scale applications.

As OOPs are a popular topic in programming interviews, it is essential for candidates to have a thorough understanding of OOPs concepts. Here are some top interview questions on OOPs concepts that may help candidates prepare for their programming interviews:

1. What is inheritance in OOPs, and how is it useful?
2. Explain the difference between abstraction and encapsulation in OOPs.
3. What is polymorphism in OOPs, and how is it achieved in programming?
4. What is the significance of the ‘final’ keyword in OOPs?
5. What are the advantages of using OOPs in software development?
6. Explain the concept of interface in OOPs.
7. What is the difference between an abstract class and an interface in OOPs?
8. What is the difference between a class and an object in OOPs?
9. How do you implement encapsulation in OOPs?
10. What is the role of constructors in OOPs, and what are the different types of constructors available in Java?

By having a clear understanding of OOPs concepts and answering these questions, candidates can demonstrate their programming knowledge and skills, thereby increasing their chances of getting hired for programming roles.

What are the key concepts of OOPs?

The key concepts of OOPs are:

• Encapsulation: The data and methods are encapsulated together in an object, providing data security and preventing external interference.
• Inheritance: The ability to derive new classes from existing ones, inheriting their properties and behavior, and modifying them if necessary.
• Polymorphism: The ability to use a single interface to represent different types of data or behavior.
• Abstraction: The ability to hide complex implementation details and present only the necessary and relevant information to the user.

What are the advantages of OOPs?

4. The advantages of OOPs are:

• Modularity: Objects can be easily reused in different parts of the software, reducing code duplication and increasing modularity.
• Maintainability: OOPs make it easier to maintain the software as the code is organized in a structured way, with a clear separation of concerns and modular design.
• Flexibility: OOPs allow for flexibility in designing and modifying the software by providing features such as encapsulation, inheritance, and polymorphism.
• Extensibility: OOPs make it easier to add new features or modify the existing ones without breaking the existing code.

What are the disadvantages of OOPs?

5. The disadvantages of OOPs are:

• Complexity: OOPs can be more complex than other programming paradigms, requiring more effort and skills to master.
• Overhead: OOPs may introduce some overhead in terms of memory usage and runtime performance, especially for small and simple programs.
• Learning curve: OOPs may have a steep learning curve for beginners, requiring a deeper understanding of the concepts and principles.

What are some examples of OOPs programming languages?

6. Some examples of OOPs programming languages are:

• Java
• C++
• Python
• Ruby
• Swift
• C#
• Objective-C

In conclusion, OOPs is a programming paradigm that uses objects to organize and structure the software. It provides several advantages such as modularity, maintainability, flexibility, and extensibility, but also has some disadvantages such as complexity, overhead, and learning curve. Several programming languages such as Java, C++, Python, and Ruby support OOPs.

What is a Class?

A class is a fundamental concept in object-oriented programming (OOP). It is a template or blueprint that defines a set of attributes (data members) and methods (member functions) that describe the behaviour of objects that are created from it.

In simpler terms, a class can be thought of as a cookie cutter that defines the shape and size of a cookie. In the same way, a class defines the structure and behaviour of objects.

Classes provide a way to encapsulate related data and function into a single unit. They allow us to create objects that have specific properties and behaviours, and they can be used to model real-world entities in software applications.

In addition to data members and member functions, a class may also contain other elements such as constructors, destructors, and access modifiers. Constructors are special member functions that are called when an object is created, while destructors are called when an object is destroyed. Access modifiers, such as public, private, and protected, define the level of access that other classes and functions have to the data and functions within a class.

Classes can be used to create objects in a variety of programming languages, including C++, Java, Python, and others. Once a class is defined, objects can be created from it by calling its constructor function. Each object created from a class is known as an instance of that class.

Overall, classes are a fundamental concept in OOP and provide a way to organize code into reusable and modular units. They allow developers to create complex applications by modelling real-world entities and describing their behaviour using objects and methods.

What is an Object?

In object-oriented programming (OOP), an object is an instance of a class. It represents a real-world entity with a specific set of properties (data members) and actions (member functions) that can be performed on those properties.

Objects are created from classes by instantiating them using the constructor function. Each instance of a class has its own set of data members and can perform its own set of actions, independent of other instances of the same class.

For example, imagine a class called "Car" that has data members such as "make", "model", and "year", as well as member functions such as "start_engine()" and "accelerate()". An object created from this class might represent a specific car with a make of "Toyota", a model of "Camry", and the year "2019". This object would have its own set of values for the data members and could perform actions such as starting the engine and accelerating, independent of any other objects created from the same class.

In OOP, objects are important because they allow us to model real-world entities and manipulate data in a way that is more intuitive and organized than traditional procedural programming. They also provide a way to encapsulate data and functionality, making it easier to manage and reuse code.

Overall, objects are a key concept in OOP, representing the instances of classes that encapsulate data and functionality. They allow us to create modular and reusable code that can be used to model real-world entities and manipulate data in a more intuitive and organized way.

What is Encapsulation?

Encapsulation is one of the four fundamental principles of object-oriented programming (OOP). It is the process of combining data and functions that operate on that data within a single unit or class while restricting access to the data from the outside world. The purpose of encapsulation is to protect the integrity of the data and to provide a clear separation of concerns between different parts of the code.

Encapsulation is implemented through two key processes:

1. Data Hiding: This refers to the concept of hiding the internal details of an object from the outside world. In other words, data members of an object are marked as private or protected so that they cannot be accessed or modified directly from outside the class. Only the member functions of the class can access and modify the private or protected data members. This ensures that the data is protected from accidental or intentional modifications by external entities, which could lead to inconsistencies or bugs.

For example, consider a class called "BankAccount" that has private data members such as "balance" and "accountNumber". These data members are hidden from the outside world and can only be accessed or modified through member functions such as "deposit()" and "withdraw()".

2. Bundling of data and methods together: This refers to the idea that data and the functions that operate on that data should be bundled together within a single unit or class. This ensures that the behavior of the data is closely tied to the data itself, which makes it easier to maintain and understand. By encapsulating the data and functions together, it becomes easier to manage changes to the code, and reduces the likelihood of errors or inconsistencies.

For example, consider a class called "Employee" that has private data members such as "name", "age", and "salary", as well as member functions such as "getSalary()" and "setSalary()". The data and the functions that operate on that data are bundled together within the "Employee" class, providing a clear separation of concerns between different parts of the code.

Overall, encapsulation is a powerful concept in object-oriented programming that enables us to create robust, modular, and maintainable code. By combining data and functions within a single unit, and restricting access to that data from the outside world, we can create code that is more reliable and easier to understand and maintain.

What is Abstraction?

Abstraction is the process of hiding complex implementation details while only showing the necessary information to the user. It is one of the fundamental concepts of Object-Oriented Programming (OOP). Abstraction can be implemented using classes and interfaces in programming languages such as Java, C++, Python, etc.

In simple terms, abstraction allows a user to interact with an object without worrying about the underlying details of how it works. For example, when you use a television remote, you do not need to know how the remote actually communicates with the TV, you just need to know which buttons to press to perform certain actions.

In programming, abstraction is achieved by creating abstract classes or interfaces that provide a common set of methods or properties that can be used by other classes. An abstract class is a class that cannot be instantiated and is typically used as a base class for other classes to inherit from. An interface is a collection of abstract methods and constants that can be implemented by any class.

Using abstraction, developers can write code that is more flexible, maintainable, and scalable. It also makes it easier to change the implementation details of a class without affecting the code that uses it.

Overall, abstraction is an important principle in OOP that allows developers to create complex software systems that are easy to use, understand, and modify.

What is Polymorphism?

Polymorphism is a key concept in Object-Oriented Programming (OOP) that allows objects of different classes to be treated as if they are the same type. The term "polymorphism" comes from the Greek words "poly" (meaning "many") and "morph" (meaning "form").

There are two types of polymorphism in OOP:

Compile-time Polymorphism:

1. Also known as static polymorphism, it occurs when the compiler knows which method to call during compile-time based on the number, type, and order of arguments passed to it. Examples of compile-time polymorphism include function overloading and operator overloading.

Function overloading allows a class to have multiple methods with the same name, but different parameters. The correct method to call is determined at compile-time based on the arguments passed to the function. Operator overloading allows operators such as +, -, *, /, and % to be redefined for user-defined classes.

Runtime Polymorphism:

2. Also known as dynamic polymorphism, it occurs when the method to be called is determined at runtime, based on the actual type of the object. Examples of runtime polymorphism include virtual functions and abstract classes.

Virtual functions are functions that are declared in a base class and are overridden by derived classes. When a virtual function is called on an object, the method that is executed is determined at runtime based on the actual type of the object. This allows objects of different classes to be treated as if they are the same type.

Abstract classes are classes that cannot be instantiated and are used as base classes for other classes to inherit from. They can contain pure virtual functions, which are virtual functions without an implementation. Any class that inherits from an abstract class must provide an implementation for its pure virtual functions.

Polymorphism is an important concept in OOP as it allows code to be more flexible, reusable, and maintainable. It also allows developers to write code that is more intuitive and easier to understand.

What is Inheritance? What is its purpose?

Inheritance is one of the core concepts of Object Oriented Programming (OOP) that allows classes to inherit properties and methods from their parent class. The derived class, also known as the subclass or child class, inherits the characteristics of the base class, also known as the parent or superclass. Inheritance is based on the idea of reusability, as it allows programmers to define a new class based on an existing class and modify it to suit the specific needs of their program.

The purpose of inheritance is to enable code reusability, reduce redundancy, and simplify code maintenance. Instead of redefining properties and methods in each class, they can be defined once in the parent class and inherited by the child classes. This also makes the code easier to maintain as changes can be made in one place and applied to all derived classes.

Inheritance also facilitates polymorphism, which is the ability of objects of different classes to be used interchangeably. Inheritance allows subclasses to implement methods that are already defined in the superclass, or override them to provide a different implementation. This enables objects of the subclass to be used in the same way as objects of the superclass, without the need to modify the existing code.

Inheritance is implemented using the 'extends' keyword in most OOP languages, such as Java and C++. The subclass extends the parent class, and all public and protected properties and methods of the parent class are inherited by the child class. Inheritance can be single or multiple, depending on the language and the design of the program.

In summary, inheritance is a fundamental concept in OOP that allows classes to inherit properties and methods from their parent class, enabling code reusability, reducing redundancy, and facilitating polymorphism.

What are access specifiers? What is their significance in OOPs?

Access specifiers play a crucial role in achieving encapsulation and data hiding in object-oriented programming.

In object-oriented programming, data members and member functions of a class can have access specifiers which define their visibility and accessibility outside of the class. There are three types of access specifiers in most object-oriented programming languages: Public, Private, and Protected.

Public Access Specifier:

1. Public access specifier allows the data members and member functions of a class to be accessed from anywhere in the program, including outside of the class. This means that the data members and member functions can be accessed and modified by any part of the program that has access to the object.

Private Access Specifier:

2. Private access specifier allows the data members and member functions of a class to be accessed only from within the same class. This means that the data members and member functions cannot be accessed or modified by any other part of the program.

Protected Access Specifier:

3. Protected access specifier allows the data members and member functions of a class to be accessed from within the same class and from its derived classes. This means that the data members and member functions can be accessed and modified by any part of the program that has access to the derived class.

The significance of access specifiers in object-oriented programming lies in their ability to control the visibility and accessibility of the data members and member functions of a class. This helps in achieving encapsulation, where the data members and member functions of a class are hidden from the outside world and can only be accessed through the public interface provided by the class.

By making the data members private, we can ensure that they are not directly accessible from outside of the class, and can only be accessed through the member functions of the class. This helps in maintaining the integrity of the data and avoids unauthorized modifications.

In conclusion, access specifiers play a crucial role in achieving encapsulation and data hiding in object-oriented programming. They allow us to control the visibility and accessibility of the data members and member functions of a class, which helps in maintaining the integrity of the data and avoids unauthorized modifications.

What other paradigms of programming exist besides OOPs?

1. Imperative Programming Paradigm: This paradigm works by changing the program state through assignment statements. The main focus is on how to achieve the goal. The following programming paradigms come under this category:

• Procedural Programming Paradigm: This programming paradigm is based on the procedure call concept. Procedures, also known as routines or functions, are the basic building blocks of a program in this paradigm.

• Object-Oriented Programming or OOP: In this paradigm, we visualize every entity as an object and try to structure the program based on the state and behavior of that object.

• Parallel Programming: The parallel programming paradigm is the processing of instructions by dividing them into multiple smaller parts and executing them concurrently.

2. Declarative Programming Paradigm: This paradigm focuses on what is to be executed rather than how it should be executed. In this paradigm, we express the logic of a computation without considering its control flow. The declarative paradigm can be further classified into:

• Logical Programming Paradigm: It is based on formal logic where the program statements express the facts and rules about the problem in the logical form.

• Functional Programming Paradigm: Programs are created by applying and composing functions in this paradigm.

• Database Programming Paradigm: To manage data and information organized as fields, records, and files, database programming models are utilized.

3. Event-Driven Programming Paradigm: In this paradigm, the program's execution is driven by events that occur at runtime, such as user actions or system notifications.

4. Concurrent Programming Paradigm: This paradigm deals with the simultaneous execution of multiple tasks in a program. It involves synchronization, communication, and coordination between these tasks.

5. Aspect-Oriented Programming Paradigm: This paradigm aims to increase modularity and separation of concerns in a program by allowing the definition of aspects that cut across multiple modules.

6. Metaprogramming Paradigm: This paradigm involves writing programs that generate other programs, or manipulate the source code of other programs.

Structured Programming and Object-Oriented Programming (OOP) are two different programming paradigms.

Structured Programming is a programming paradigm that focuses on using structured code and avoiding the use of unstructured constructs such as the infamous "goto" statement. This paradigm mainly uses procedures, functions, and loops to achieve the program's objectives. The data and functions are not encapsulated together in a single entity. Instead, the data is passed as arguments to the functions.

Structured Programming:

• Focuses on the process of solving a problem

• Uses only functions or procedures for code organization

• Data is passed between functions or procedures as parameters

• Emphasizes on top-down design and modular programming

• No concept of classes or objects

• Access to data is often global

• Less flexible in handling complex problems

• Code reusability is limited

Object-Oriented Programming, on the other hand, is a programming paradigm that is centered around objects that contain data and the methods that operate on that data. This paradigm aims to model real-world entities and focuses on the behavior and interactions of the objects in a system. The data and functions are encapsulated together into a single entity, the class.

Object Oriented Programming:

• Focuses on objects and their behavior to solve a problem

• Uses classes to organize code, which contain both data and functions

• Encapsulates data within the classes and provides controlled access through methods

• Emphasizes on bottom-up design and reuse of existing code

• Data hiding and abstraction are important concepts

• Encourages inheritance and polymorphism for code reuse and flexibility

• Code is modular, extensible and reusable

• Provides a better approach to handling complex problems.

In summary, the main difference between Structured Programming and OOP is that Structured Programming focuses on the procedure and functions while OOP focuses on objects and their interactions.

What are some commonly used Object Oriented Programming Languages?

Some commonly used Object Oriented Programming languages are:

1. Java: A popular language used for developing desktop, web and mobile applications. It is an object-oriented language that is easy to learn and has a large user base.

2. C++: A powerful language used for developing operating systems, embedded systems, and large-scale applications. It is an extension of C language and supports both procedural and object-oriented programming.

3. Python: A versatile language used for web development, data analysis, machine learning, and scientific computing. It supports both procedural and object-oriented programming paradigms.

4. Ruby: A dynamic, interpreted language that emphasizes on simplicity and productivity. It is commonly used for web development and has a large number of open-source libraries.

5. PHP: A server-side scripting language used for developing web applications. It supports object-oriented programming and is widely used for content management systems like WordPress and Drupal.

6. Swift: A modern language developed by Apple for developing applications on iOS, macOS, and watchOS. It is an object-oriented language that is easy to learn and has a concise syntax.

7. C#: A language developed by Microsoft for developing desktop and web applications on the .NET platform. It is similar to Java and supports object-oriented programming, along with other programming paradigms.

What are the different types of Polymorphism?

There are two types of polymorphism:

1. Compile-time Polymorphism: Also known as static polymorphism, this type of polymorphism is resolved during the compile-time by the compiler. This type of polymorphism is achieved by function overloading or operator overloading.

2. Run-time Polymorphism: Also known as dynamic polymorphism, this type of polymorphism is resolved during the run-time by the compiler. This type of polymorphism is achieved by method overriding using virtual functions.

What is the difference between overloading and overriding?

Overloading and overriding are both examples of polymorphism in object-oriented programming, but they have different meanings.

Overloading occurs when a class has multiple methods with the same name but different parameters (number, type, or order of parameters). The compiler decides which method to call based on the number, type, and order of the arguments passed. Overloading happens at compile-time and is called compile-time polymorphism or static polymorphism.

Overriding, on the other hand, occurs when a derived class provides its implementation of a method that is already defined in the parent class. The signature (name, parameters, and return type) of the method in the child class must match the signature of the method in the parent class. The method in the child class is said to override the method in the parent class. Overriding happens at runtime and is called runtime polymorphism or dynamic polymorphism.

In summary, overloading allows different methods to have the same name, but different parameters, while overriding allows a child class to provide its implementation of a method already defined in the parent class.

Are there any limitations on Inheritance?

there are certain limitations on inheritance, some of them are:

1. Inheriting Private Members: A derived class cannot access the private members of its base class.

2. Inheriting Constructors: Constructors cannot be inherited by derived classes. However, constructors of a base class can be called using the derived class.

3. Multiple Inheritance: If multiple inheritance is used, it can cause conflicts between two or more base classes having the same name or implementation of a method.

4. Diamond Problem: It is a problem that arises in the case of multiple inheritance when two or more base classes have a common base class. The derived class is unable to identify which base class to inherit and this results in ambiguity.

5. Tight Coupling: Inheritance can lead to tight coupling between classes, which can make the code hard to maintain and modify. Any changes in the base class will affect all the derived classes.

These limitations should be considered while designing the inheritance hierarchy to avoid any complications.

What different types of inheritance are there?

There are several types of inheritance in object-oriented programming:

1. Single inheritance: A class is derived from only one base class.

2. Multiple inheritance: A class is derived from two or more base classes.

3. Multilevel inheritance: A derived class is created from another derived class, which is itself derived from a base class.

4. Hierarchical inheritance: Multiple classes are derived from a single base class.

5. Hybrid inheritance: This is a combination of multiple inheritance and multilevel inheritance.

6. Multipath inheritance: This is when a derived class is derived from more than one base class, and those base classes have a common base class.

What is an interface?

An interface is a programming concept that defines a set of methods and/or properties that a class must implement if it implements the interface. It serves as a contract between the class and its user, ensuring that the class implements the required functionality in a standardized way.

In Java, an interface is defined using the interface keyword, and it contains method signatures without any implementation code. A class that implements an interface must provide an implementation for each method defined in the interface.

Interfaces are used to achieve abstraction, which is a fundamental principle of object-oriented programming. By programming to an interface rather than a concrete implementation, code can be more flexible and easily maintainable. Additionally, interfaces are often used to define APIs, allowing multiple implementations to work together seamlessly.

In summary, an interface is a blueprint for implementing a set of methods and/or properties, and it provides a standardized way for classes to interact with each other.