CODEWITHSUNDEEP
kotlinkotlin-extension
pRaNaY
pRaNaY

Reputation: 25312

How to check "instanceof " class in Kotlin?

In Kotlin class, I have method parameter as object (See Kotlin doc here ) for class type T. As object I am passing different classes when I am calling method. In Java we can able to compare class using instanceof of object which class it is.

So I want to check and compare at runtime which Class it is?

How can I check instanceof class in Kotlin?

Upvotes: 273

Views: 236630

Answers (9)

Mahozad
Mahozad

Reputation: 24472

If you have a collection of objects, you can also keep those that are specific instance:

interface Fruit
class Peach: Fruit
class Watermelon: Fruit

val fruits = listOf(
    Peach(),
    Peach(),
    Watermelon(),
    Peach(),
    Watermelon()
)

val peaches = fruits.filterIsInstance(Peach::class.java)

Upvotes: 0

Cevin Ways
Cevin Ways

Reputation: 984

You can read Kotlin Documentation here https://kotlinlang.org/docs/reference/typecasts.html . We can check whether an object conforms to a given type at runtime by using the is operator or its negated form !is, for the example using is: 

fun <T> getResult(args: T): Int {
    if (args is String){ //check if argumen is String
        return args.toString().length
    }else if (args is Int){ //check if argumen is int
        return args.hashCode().times(5)
    }
    return 0
}

then in main function i try to print and show it on terminal :

fun main() {
    val stringResult = getResult("Kotlin")
    val intResult = getResult(100)

    // TODO 2
    println(stringResult)
    println(intResult)
}

This is the output

6
500

Upvotes: 3

&#193;lvaro Ag&#252;ero
&#193;lvaro Ag&#252;ero

Reputation: 4800

Other solution : KOTLIN

val fragment = supportFragmentManager.findFragmentById(R.id.fragment_container)

if (fragment?.tag == "MyFragment")
{}

Upvotes: -8

The Bala
The Bala

Reputation: 1313

You can check like this

 private var mActivity : Activity? = null

then

 override fun onAttach(context: Context?) {
    super.onAttach(context)

    if (context is MainActivity){
        mActivity = context
    }

}

Upvotes: 5

Avijit Karmakar
Avijit Karmakar

Reputation: 9388

We can check whether an object conforms to a given type at runtime by using the is operator or its negated form !is.

Example:

if (obj is String) {
    print(obj.length)
}

if (obj !is String) {
    print("Not a String")
}

Another Example in case of Custom Object:

Let, I have an obj of type CustomObject.

if (obj is CustomObject) {
    print("obj is of type CustomObject")
}

if (obj !is CustomObject) {
    print("obj is not of type CustomObject")
}

Upvotes: 37

methodsignature
methodsignature

Reputation: 4392

Combining when and is:

when (x) {
    is Int -> print(x + 1)
    is String -> print(x.length + 1)
    is IntArray -> print(x.sum())
}

copied from official documentation

Upvotes: 79

Terril Thomas
Terril Thomas

Reputation: 1506

Try using keyword called is Official page reference

if (obj is String) {
    // obj is a String
}
if (obj !is String) {
    // // obj is not a String
}

Upvotes: 10

nhaarman
nhaarman

Reputation: 100358

Use is. 

if (myInstance is String) { ... }

or the reverse !is

if (myInstance !is String) { ... }

Upvotes: 484

ice1000
ice1000

Reputation: 6569

You can use is:

class B
val a: A = A()
if (a is A) { /* do something */ }
when (a) {
  someValue -> { /* do something */ }
  is B -> { /* do something */ }
  else -> { /* do something */ }
}

Upvotes: 10

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