Can't compile a simple Properties loop demo

Hi there,

The following code failed to compile

package test fun main(args : Array<String>) {   for ((name, value) in System.getProperties())           if (name.startsWith("java"))            println("Sys prop: $name=$value") }

I get this error:

ERROR: /Users/zemian/projects/sandbox/kotlin-demo/src/main/kotlin/Test.kt: (4, 12) None of the following functions can be called with the arguments supplied: public final fun jet.String.startsWith(prefix : jet.String) : jet.Boolean defined in kotlin public final fun jet.String.startsWith(prefix : jet.String, toffset : jet.Int) : jet.Boolean defined in kotlin public final fun jet.String.startsWith(ch : jet.Char) : jet.Boolean defined in kotlin

I am using Maven and <kotlin.version>0.4.68</kotlin.version> dependency


The diagnostics are unhelpful, sorry about that. The problem is that Properties extends Hashtable<Object,Object>, so your 'name' variable is of type Any, not String. You can cast it or call toString()

Ah, I should have paid attenttion to that. Thanks Andrey.

However another question I have when I try to loop through the stringPropertyNames() set (which is a String set this time), I also get errors.


for (name in System.getProperties().stringPropertyNames())

Errors received:

(6, 19) : For-loop range must have an iterator() method

(6, 41) : Only safe (?.) or non-null asserted (!!.) calls are allowed on a nullable receiver of type java.util.Properties?

I think I am missing something silly again. Any hints?


Kotlin think that all things came from java are Nullable.

Read this

To fix your problem look here

similar quation How do I access String.CASE_INSENSITIVE_ORDER from Kotlin? - #2 by B7W

Best regards, B7W

Thanks for the links B7W.

Reading it through, and I got it to run like this:


for (name in System.getProperties()!!.stringPropertyNames()!!.iterator())
          if (name!!.startsWith(“java.vendor”))
               println(“Sys prop: $name=${System.getProperty(name)}”)

I understand the intention of Kotlin on avoidance of NPE, but forcing such rule makes using Java integration seems painful and ugly.

I do see that you point to article using “external annotation”, however I don’t see instructions on how to do it without the IDE?