Mostly Asked OOP's Interview Questions
Here, is the list of some of the most commonly asked object-oriented programming (OOP's) interview questions and answers.
1. What is Object Oriented Programming ?
In simple words object oriented programming is a programming type that is based on objects rather than just functions and procedures. Here, objects are considered as a real world entities like table, dog, cat etc. This objects have some states and behaviors.
2. What are the advantages of OOP's ?
Using OOPs our code becomes more simpler, secure, reusable and modifiable.
- Like using Inheritance we can reuse our existing code which will improve the performance of the application.
- Using encapsulation we can bind data and methods together in single unit which increases the security of an application.
- We can hide unnecessary details from the end user by showing only important details using abstraction.
- One object can take different forms using polymorphism which makes our code more flexible.
3. What are the most popular OOP's languages?
Java
C++
Python
C#
Ruby
and many more....
4. What is a Class?
Class is like a template or blueprint to create an objects. We can also use a class as as a user defined datatype. It binds data members and member functions together.
5. What is Object?
An object is a real world entity like a cat, dog, bike etc. It has both sates and behaviors here, states represents its data and behaviors represents its functionality.
6. What is Constructor?
Constructor is a special type of method whose name is same as its class name. It is automatically called when object of the class is created and it is used for initializing an objects.
7. What is the difference between class and object?
| Class | Object |
|---|---|
| Class is a template or blueprint of an object | Object is a real world entity |
| Class is like a category | And object is like a item in that category |
| Class is a logical entity and does not take memory space when created | Object is a physical entity, So it takes memory space when created |
8. What is a superclass or base class?
A superclass or base class is a class from which subclass or child class is created. It acts like a parent of other classes.
9. What is a subclass or derived class?
A subclass or derived class is a class which is inherited from another class. It is also called as a child class. We can create a sublass by inheriting it from other class(using "extends" keyword) or from interface (using "implements" keyword).
10. What are the main features of OOP's ? Explain?
There are four main features of OOP's.... Inheritance, Encapsulation, Polymorphism and Data Abstraction.
After that you can explain above four features one by one.
11. What is inheritance means ?
In simple words, In inheritance we create one class using another class. The class which is inherited from other class can access the all data of that class. So, inheritance allows code reusability.
12. What is polymorphism?
In OOP's Polymorphism means ability to exist in multiple forms. for example: if we have class called a books and it have method called author but we cannot define it because different books have different authors. We can define method in the subclass with different definitions for different books.
13. What is encapsulation?
Encapsulation is a nothing but a binding data and code together into a single unit. For Example: To achieve data abstraction... Within a class we need to make variables private and to access that variable we have to provide getter and setter methods. Here, The setter method is used to initialize or update the variable with a given value, and the getter method is used to retrieve or return the value of that variable.
14. Explain what is abstraction with real life example?
Abstraction means hiding internal implementations from user and only showing important details to the user or we can say abstraction means only showing necessary details to the user by hiding internal implementation.
For Example: We all use an ATM machine to withdraw money but we don't know how internally it works that is nothing but a abstraction.
15. What is method overloading?
Class having two or more methods with same name and with different parameters is nothing but a method overloading.
16. What is method overriding?
If child class is not satisfied with parent class method definition then child class is allowed to redefine that methods based on its requirement then this called as a method overriding. Here, the overridden method must have same method signature(Name and parameters) as a parent class method.
While preparing for Java interviews, knowing these OOP's interview questions is crucial. Thank you for reading this article so far. If you have any doubts, please discuss them in the comment section below and share this article with your friends and colleagues.
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