Introduction

Are you a Kotlin developer that wants to learn Dart, or a Dart developer that wants to learn Kotlin, with the least possible effort? Then you are in the right place!

Important note: info boxes that does not specify if they refer to Kotlin or Dart by default are referring to Dart. for example:

semicolon at end of lines

This document is based on

Dart version 2.18.0
Kotlin 1.7.10

Kotlin to Dart transpiler

If you are interested into a tool to help porting Kotlin code to Dart try our kotlin2dart transpiler.

Experimenting with code

You can experiment with Dart code online in DartPad

You can experiment with Kotlin code online in Kotlin Playground

Hello World

The basic Dart syntax is very similar to Java.

Kotlin

public fun main() { //public is optional
    var w = "world"
    print("Hello $w") //output "Hello world"
}

Dart

void main() {
    var w = 'world';
    print('Hello $w'); //output 'hello world'
}

semicolon at end of lines

Dart requires a semicolon (;) at the end of code lines. In Kotlin they are optional

single quotes for strings

Dart allows both single and double quotes for defining string literals. In Kotlin double quotes are required while single quotes define character literals

no public, protected, private

Dart doesn’t have the keywords public, protected, and private. If an identifier starts with an underscore (_), it’s private to its library.

string interpolation works the same way

Dart see docs. Kotlin see docs

var works the same way

Dart is strongly typed with support for type inference like Kotlin

Variables

Kotlin

    var a = 1               //variable, type inferred
    var aa:Int = 1          //variable, type explicit

    val b = 2               //Read-only variable, type inferred
    val bb:Int = 2          //Read-only variable, type explicit

    const val c = 3         //compile-time constant, type inferred
    const val cc:Int = 3    //compile-time constant, type explicit

    var str:String?= null    //nullable variable

    lateinit var d:String    //initialized later

Dart

    var a = 1;              //variable, type inferred
    int aa = 1;             //variable, type explicit

    final b = 2;            //Read-only variable, type inferred
    final int bb = 2;       //Read-only variable, type explicit

    const c = 3;            //compile-time constant, type inferred
    const int cc = 3;       //compile-time constant, type explicit

    String? str;            //nullable variable, by default initialized to null

    late String d;          //initialized later

final instead of val

Dart uses the final keyword for identifying readonly variables. Kotlin uses the val keyword

const instead of const val

Dart uses the const keyword for identifying compile-time constants. Kotlin uses the combination of keywords const val

const is a more extended concept

see const variables and const constructors in Dart documentation.

nullable variable are by default initialized to null

Dart automatically initializes to null nullable variables

late instead of lateinit

Kotlin lateinit variables are called late variables in Dart