abstract class

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syntax:

abstract class Name{

    abstract fun methodName()

}

===============

abstract class - It is uses an abstract keyword and a class keyword followed by the class name and optional class header. The body of an abstract class may contain one or more abstract methods. Once the class or the method is declared abstract,  you don't need to specify it with an open keyword. Remember that the open keyword is used when you want to extend that class to another class.

================

import kotlin.math.PI

import kotlin.math.pow

fun main(){

    val obj = MyCircle()

    obj.calculateArea()

}

abstract class Circle(var radius: Double = 0.0){

    abstract fun calculateArea()

}

class MyCircle: Circle(){

    override fun calculateArea(){

        radius = 3

        val squaredRadius = radius.pow(2.0)

        val answer = PI * squaredRadius

        println("answer: $answer")

    }

}

===================

Result:

answer: 28.274333882308138


Note: You can override a non-abstract open member with abstract member


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