Explicit casting

To cast a reference to a type explicitly, we use the as operator. Just as in Java, this operation will throw ClassCastException if the cast cannot be performed legally:

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

The null value cannot be cast to a type that is not defined as nullable. So, the previous example would have thrown an exception if the value was null. To cast to a value that can be null, we simply declare the required type as nullable, as we would for a reference:

    val string: String? = any as String 

Remember that if a cast fails, then a ClassCastException exception will be thrown. If we want to avoid the exception, and instead have a null value if the cast fails, then we can 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:

 val any = "/home/users"
 val string: String? = any as? String
 val file: File? = any as? File