Hands-On Object-Oriented Programming with Kotlin

Abstract functions

An abstract function is a function without a function body. To understand this concept, let's take the example of the Shape class:

abstract class Shape(val name: String) {    init {         println("Drawing $name")     }     open fun draw(){}     open fun getArea() : Double{ return 0.0 } } 

The Shape abstract class contains two normal functions: draw and getArea. Both functions are open and available for inheritance. Having non-abstract functions in an abstract class, however, does have some drawbacks. If a function is a normal or non-abstract function, it must provide a function body even if it is empty. If a child class inherits a parent class, it won't know whether it is necessary to provide an implementation of the inherited functions.