Top 10 Interview Questions on OOPS
.Net Interview Questions and Answers on OOPS
1. What is an Object in OOPS?
An object is a software bundle of variables and related methods. Objects are related to real life scenario. Class is the general thing and object is the specialization of general thingObjects is
instance of classes.
Declaration of an Object in OOPs
ClassName objectName=new ClassName();
E.g.: Person objPerson= new Person();
An object is characterized by concepts like:
2. What is an Attribute in OOPs?
• Attributes define the characteristics of a class.
• The set of values of an attribute of a particular object is called its state.
• In Class Program attribute can be a string or it can be a integer
3. What is a Behavior in OOPS?
• Every object has behavior
• In C#, behaviors of objects are written in methods.
• If a behavior of an object needs to be performed, then the corresponding method is called.
4. What is an Identity in OOPS?
• Each time an object is created the object identity is been defined.
• This identity is usually created using an identifier which is derived from the type of item
5. What is Encapsulation in OOPS?
• Encapsulation is one of the fundamental principles of object-oriented programming.
• Encapsulation is a process of hiding all the internal details of an object from the outside world
• Encapsulation is the ability to hide its data and methods from outside the world and only expose data and methods that are required
• Encapsulation is a protective barrier that prevents the code and data being randomly accessed by other code or by outside the class
• Encapsulation gives us maintainability, flexibility and extensibility to our code.
• Encapsulation makes implementation inaccessible to other parts of the program and protect from whatever actions might be taken outside the function or
• Encapsulation provides a way to protect data from accidental corruption
• Encapsulation hides information within an object
• Encapsulation is the technique or process of making the fields in a class private and providing access to the fields using public methods
• Encapsulation gives you the ability to validate the values before the object user change or obtain the value
• Encapsulation allows us to create a "black box" and protects an objects internal state from corruption by its clients.
There are two ways to create a validation process.
1. Using Assessors and Mutators
2. Using properties
Benefits of Encapsulation
• In Encapsulation fields of a class can be read-only or can be write-only
• A class can have control over in its fields
• A class can change data type of its fields anytime but users of this class do not need to change any code
6. What is Inheritance in OOPS?
• Inheritance, together with encapsulation and polymorphism, is one of the three
primary characteristics (concept) of object-oriented programming
• Inheritance enables you to create new classes that reuse, extend, and modify
the behavior that is defined in other classes
• The Class whose methods and variables are defined is called super class or base
• The Class that inherits methods and variables are defined is called sub class
or derived class
• Sometimes base class known as generalized class and derived class known as
• Keyword to declare inheritance is “:” (colon) in visual c#
Benefits of using Inheritance
• Once a behavior (method) or property is defined in a super class(base
class),that behavior or property is automatically inherited by all subclasses (derived class).
• Code reusability increased through inheritance
• Inheritance provide a clear model structure which is easy to understand without
• Using inheritance, classes become grouped together in a hierarchical tree
• Code are easy to manage and divided into parent and child classes
7. What is Polymorphism in OOPS?
• Polymorphism is one of the primary characteristics (concept) of object-oriented
• Poly means many and morph means form. Thus, polymorphism refers to being able
to use many forms of a type without regard to the details
• Polymorphism is the characteristic of being able to assign a different meaning
specifically, to allow an entity such as a variable, a function, or an object to have more than one form
• Polymorphism is the ability to process objects differently depending on their
• Polymorphism is the ability to redefine methods for derived classes.
Types of Polymorphism
• Compile time Polymorphism
• Run time Polymorphism
8. What is Compile Time Polymorphism in OOPS?
• Compile time Polymorphism also known as method overloading
• Method overloading means having two or more methods with the same name but with
9. What is Run Time Polymorphism in OOPS?
• Run time Polymorphism also known as method overriding
• Method overriding means having two or more methods with the same name , same
signature but with different implementation
10. What is Access Modifier in OOPS?
Access modifiers determine the extent to which a variable or method can be accessed from another class or object
The following five accessibility levels can be specified using the access modifiers
• Protected internal