OOP

Question 1

Abstraction

Answer 1

Data Abstraction is the property by virtue of which only the essential details are displayed to the user. The trivial or non-essential units are not displayed to the user. Ex: A car is viewed as a car rather than its individual components.

Consider a real-life example of a man driving a car. The man only knows that pressing the accelerators will increase the car speed or applying brakes will stop the car, but he does not know how on pressing the accelerator, the speed is actually increasing.

Question 2

Encapsulation

Answer 2

It is defined as the wrapping up of data under a single unit. It is the mechanism that binds together the code and the data it manipulates. Another way to think about encapsulation is that it is a protective shield that prevents the data from being accessed by the code outside this shield.

Question 3

Inheritance

Answer 3

It is the mechanism in Java by which one class is allowed to inherit the features (fields and methods) of another class. We are achieving inheritance by using extends keyword. Inheritance is also known as “is-a” relationship.

Reusability: Inheritance supports the concept of “reusability”, i.e. when we want to create a new class and there is already a class that includes some of the code that we want, we can derive our new class from the existing class. By doing this, we are reusing the fields and methods of the existing class.

Question 4

Polymorphism

Answer 4

It refers to the ability of object-oriented programming languages to differentiate between entities with the same name efficiently. This is done by Java with the help of the signature and declaration of these entities. The ability to appear in many forms is called polymorphism.

Overloading - allows different methods to have the same name, but different signatures where the signature can differ by the number of input parameters or type of input parameters, or a mixture of both.

Overriding - Overriding is a feature that allows a subclass or child class to provide a specific implementation of a method that is already provided by one of its super-classes or parent classes.

Question 5

Interface vs abstract class

Answer 5

Every single Method declared in an Interface will have to be implemented in the subclass.

Only Abstract methods have to be implemented by the subclass. An Abstract class can have normal methods with implementations.

Multiple inheritance is allowed only for interfaces. A subclass can only extend a single parent class.