Abstraction in Java in Details Step by Step

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Abstraction:

Abstraction is the process of hiding the implementation details, only showing the functionality.

In other words, Abstraction is the process to reduce complexity and taking out the important characteristics of a class.

There are two ways to achieve abstraction in java

1.     Abstract class

2.     Interface

1. Abstract class

Abstract class defines a class that contains the abstraction without providing a complete implementation of method. The abstract keyword is used for abstract class and abstract method.

Abstract classes are used if you want to create a super class that only defines the variables and methods and sub class will be accessed the variables and methods for implementation.

Rule of Abstract class.

        1.   Abstract classes may or may not contain abstract methods.

        2.   Must be declared abstract keyword if a class has at least one abstract method.

        3.     The class cannot be instantiated if abstract is declared.

        4.     Must be provided implementations of all the abstract methods, If you inherit            an abstract class.

         

         Example:

abstract class Figure {

    

      double dim1;

      double dim2;

    

      Figure(double d1,double d2){

            dim1 = d1;

            dim2 = d2;

      }

    

      abstract void area();

  }

   class Rectangle extends Figure{

    

      Rectangle(double d1,douple d2){

            super(d1,d2);

      }

      //Override area of rectangle

      void area(){

            System.out.println("area of rectangle is"+ dim1*dim2);

          

      }

   }

   class Demo{

      public static void main(String args[]){

            Figure f = new Rectangle(4,7);

            f.area();

   }

  Output:

      area of rectangle is 28

2.     Interface

The interface in java provides abstraction. We can create only abstract method in interface and can’t create implementation or method body. It is used to achieve abstraction and multiple inheritance in Java.  It has static constants and abstract methods.

Rule of Interface

1.        All interface Methods are implicitly public and abstract

2.        All variables in Interface by default constant(public, static, final).

3.        Interface Methods can not be static.

4.        Interface Methods can not be final.

5.        One Interface can extend one or more Interface.

Example:

interface Area
{
  final static float pi = 3.14f;
  float findArea(float x);
}


class Circle implements Area
{
  public float findArea(float x)
   {
     return (x*x*xpi);
   }
}


class Square implements Area
{
  public float findArea(float x)
  {
   return(x*x);
  }
}


public class InterFaceDemo
{
 public static void main(String args[])
 {
  Circle c = new Circle();
  Square s= new Square();
  Area area;
  area = c;
  System.out.println("Area of Circle is" + area.findArea(10));
  area = s;
  System.out.println("Area of Square is" + area.findArea(30));

 }