JUnit allows providing rules through a test class field or a getter method. What you annotated is in Kotlin a property though, which JUnit won’t recognize. Here are the possible ways to specify a JUnit rule in Kotlin: Through an annotated getter method From M13, the annotation processor supports annotation targets. When you write @Rule … Read more
The truth is: data classes do not play too well with inheritance. We are considering prohibiting or severely restricting inheritance of data classes. For example, it’s known that there’s no way to implement equals() correctly in a hierarchy on non-abstract classes. So, all I can offer: don’t use inheritance with data classes.
TL;DR: What is reified good for fun <T> myGenericFun(c: Class<T>) In the body of a generic function like myGenericFun, you can’t access the type T because it’s only available at compile time but erased at runtime. Therefore, if you want to use the generic type as a normal class in the function body you need … Read more
As CommonsWare mentioned, for reference add this inside the android {…} closure in the build.gradle for your app module (app level) to resolve the issue: android { … compileOptions { sourceCompatibility JavaVersion.VERSION_1_8 targetCompatibility JavaVersion.VERSION_1_8 } … }
Avoid using companion objects. Behind the hood, getter and setter instance methods are created for the fields to be accessible. Calling instance methods is technically more expensive than calling static methods. public class DbConstants { companion object { val TABLE_USER_ATTRIBUTE_EMPID = “_id” val TABLE_USER_ATTRIBUTE_DATA = “data” } Instead define the constants in object. Recommended practice … Read more
Android Studio’s UI was just hiding the error… when the error occurred, it highlighted the item in the list view, and showed an unhelpful message in the terminal view. to find the real error, select the root item in the list view so that Android Studio would display the whole build output in the terminal … Read more
sortedWith + compareBy (taking a vararg of lambdas) do the trick: val sortedList = list.sortedWith(compareBy({ it.age }, { it.name })) You can also use the somewhat more succinct callable reference syntax: val sortedList = list.sortedWith(compareBy(Person::age, Person::name))
You can simply write: val mutableList = mutableListOf<Kolory>() This is the most idiomatic way. Alternative ways are val mutableList : MutableList<Kolory> = arrayListOf() or val mutableList : MutableList<Kolory> = ArrayList() This is exploiting the fact that java types like ArrayList are implicitly implementing the type MutableList via a compiler trick.
In your code result is not changing, its var properties are changing. Refer comments below: fun copyAddress(address: Address): Address { val result = Address() // result is read only result.name = address.name // but not their properties. result.street = address.street // … return result } val is same as the final modifier in java. As … Read more
val numbers: IntArray = intArrayOf(10, 20, 30, 40, 50) See Kotlin – Basic Types for details. You can also provide an initializer function as a second parameter: val numbers = IntArray(5) { 10 * (it + 1) } // [10, 20, 30, 40, 50]