How to check “instanceof ” class in kotlin?

问题

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?

回答1:

Use is.

if (myInstance is String) { ... }

or the reverse !is

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

回答2:

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

回答3:

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")
}

回答4:

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 */ }
}

回答5:

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
}

回答6:

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
    }

}

回答7:

回答8:

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

来源：https://stackoverflow.com/questions/44098780/how-to-check-instanceof-class-in-kotlin

标签

kotlin

kotlin-extension