Kotlin - Statement Explicit casting

Introduction

To cast a reference to a type explicitly, we use the as operator.

This operation will throw a ClassCastException if the cast cannot be performed legally:

fun length(any: Any): Int { 
          val string = any as String 
          return string.length 
} 

Here, the null value cannot be cast to a type that is not defined as nullable.

It would have thrown an exception if the value was null.

To cast to a value that can be null, declare the required type as nullable:

val string: String? = any as String 

To avoid the exception, use the safe cast operator as? .

This operator will return the casted value if the target type is compatible, otherwise it will return null.

In the next example, string would be a successful cast, but file would be null:

Demo

fun main(args: Array<String>) {
    val any = "java2s.com" 
    val string: String? = any as? String 
    val file: File? = any as? File 
    //from  w ww  .j a v a 2s  .  co  m
    println(file)
}

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