Abstraction in java revision video for interview. Java By kiran

Abstraction is a process of hiding details about implementation from the user while letting them utilize the services or functions. Therefore, the user will know what an object does, but not how it does it. It is done to simplify the user interface while hiding the complex processes.

Exposing only required or important things is called abstraction
Abstraction can be done in two ways :
Abstract class
Interface
It is used for maintaining the standards of coding in the project.

Interface
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One of the java principles says that we must follow the I to C design. This means that every class should be implemented from Interface

In the industry, architect level people create interfaces and then it is given to the developers for writing classes by implementing interfaces provided

This is the best way to expose our project’s API to some other projects. For example, ICICI bank can expose methods or interfaces to various shopping carts

The interface is the same as an ordinary class but remember below points

We cannot instantiate Interface but we can create reference variables

The interface doesn't have a constructor

It can be compiled but cannot run

The interface can extend the interface

The interface can extend multiple interfaces

Abstract Class
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Abstract class is just like a normal class but with some extra features which we will see in this chapter

Abstract class can have a constructor

It can have abstract methods or concrete methods or nothing [empty class] or mix of both methods

To use abstract method of a class, we must extend the abstract class with an ordinary class or must implement all abstract methods in that ordinary class

If we don't want to implement or override that method, make those methods as abstract

If any method is abstract in a class then that class must be declared as abstract

We cannot instantiate abstract class

Multiple inheritances are not allowed in abstract class but allowed in interfaces

Abstract classes are useful if we want others to not call our class directly but through Inheritance

Abstract static final combinations are not allowed in java.

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