Java vs Kotlin


Plain Objects or Data Classes

in Kotlin:

data class Widget(var name: String, var owner: Person)

It generates getters, setters, hashCode(), equals(), toString().

You can define default parameters

class Book(val title: String,
           val price: Int = 10000,
           val desc: String = "") {

You can refer to parameters using their names

val book = Book(title = "Madame Bovary", price = 1000, desc = "Good")

You can use it for lambdas

mylist.filter { it > 4 }


You have to explicitly allow variables to be null aka. nullable-types by adding ? to the type name. Those will be checked at compile-time.

val name: String? = ""

Async Programming

In Java there are callbacks. In Kotlin there are coroutines which allow to write code in a blocking way, they are lightweight threads.

Function Types

Kotlin has proper function types.