Kotlin by Example: Classes
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As an object-oriented programming language, Kotlin supports classes. Unlike most other programming languages, Kotlin does not support member variables. It only supports member properties and member functions. |
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This is the primary constructor of a class. The Kotlin compiler will automatically generate properties for the parameters. |
class Person(val name: String, var age: Int)
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It is also possible to define properties with custom getters and setters. |
class PersonWithStats(val name: String,
val length: Double,
val weight: Double) {
val bmi get() = weight / (length * length)
}
class Rectangle(var width: Int, var height: Int) {
val area = width * height
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Kotlin also supports secondary constructors. Secondary constructors must always call the primary constructor. |
constructor(size: Int) : this(size, size) {
println("Created a square with side $size")
}
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Member functions can be defined in the way you would expect. |
fun describe() {
println(
"Rectangle: ${width}x$height (area = $area)")
}
}
fun main() {
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Kotlin does not use the |
val person = PersonWithStats("Henk", 1.80, 70.0)
println(person.bmi)
val rectangle = Rectangle(10, 20)
val square = Rectangle(20)
rectangle.describe()
square.describe()
}
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$ kotlinc main.kt -include-runtime -d main.jar
$ java -jar Main.jar
21.604938271604937
Created a square with side 20
Rectangle: 10x20 (area = 200)
Rectangle: 20x20 (area = 400)
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