Abstraction

Abstract Classes and Methods

Abstraction is the process of hiding certain complexities and showing only essential information to the user. Abstraction can be achieved with either abstract classes or interfaces.

Abstraction in Java

Abstract class: abstract class is a class with abstract keyword and we can't able to intantiate the object hence can't able to create the object using abstract class.

Abstract method: can only be used in an abstract class, and it does not have a body. The body is provided by the subclass.

An abstract class can have both abstract and regular methods

Why we need Abstract Class ?

let's understand with a very clear example

suppose we have have a shape class with a method area, now there can be multiple shapes. so we create different class as a subclass of superclass(shape) and override the area method as different shapes have different area formula.

class Shape{
  int area(int[] arr){
    // arr consists of values required to calculate the formula
    return 0;
  }
}

class Rectangle{
  int area(int[] arr){
    // length * width
    return arr[0]*arr[1];
  }
}

now in this class there is no sense in creating a object for the class shape as we did'nt know about the area formula hence in this case we use Abstract Class.

Code

abstract class Shape{
    abstract int area(int[] arr);
}

class Rectangle extends Shape{
    @Override
    int area(int[] arr){
        return arr[0]*arr[1];
    }
}

class Circle extends Shape{
    @Override
    int area(int[] arr){
        return (int)3.14*arr[0]*arr[0];
    }
}

public class Main {
    public static void main(String[] argv){
        Shape rectangle = new Rectangle();
        System.out.println("area of rectangle is: "+rectangle.area(new int[]{2,3}));
        Shape circle = new Circle();
        System.out.println("area of circle is: "+circle.area(new int[]{10}));
    }
}