NoClassDefFoundError exception when calling Java code from Kotlin

Question

I created a Kotlin project and Java class in it:

package text;

public class StringUtils {

    public static void filter(boolean flag) {
        System.out.println("Flag is " + flag);
    }
}

Then I tried to call filter method from the Kotlin code:

val exists = true;
StringUtils.filter(exists)

I didn't see any errors in my Intellij IDE but in run-time I got an exception:

Exception in thread "main" java.lang.NoClassDefFoundError: text/StringUtils
    at Person.printName(Person.kt:66)
    at PersonKt.main(Person.kt:103)
    at PersonKt.main(Person.kt)
Caused by: java.lang.ClassNotFoundException: text.StringUtils
    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:606)
    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:168)
    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
    ... 3 more

Kotlin compiler: 1.4.30
IDE: Intellij 2020.3.2
JDK: 15.0.1

I tried your code and it works fine. Make sure you put the java class inside the Java folder and not Kotlin folder. — tzortzik
– tzortzik, Commented Feb 7, 2021 at 9:52
Thank you. After I moved TextUtils into src/main/java folder the code was run properly. But I guess Intellij should display errors/warnings if I put Java class into src/main/kotlin folder and try to use it in the Kotlin code — Sergiy
– Sergiy, Commented Feb 7, 2021 at 13:45
You can configure the building system to look for both java and Kolton files in the same directories. I guess that's why the IDE doesn't show it as error. — tzortzik
– tzortzik, Commented Feb 7, 2021 at 13:50
Yes, IDEA should warn, please watch youtrack.jetbrains.com/issue/KTIJ-1233 for updates on this. — Alexey Belkov
– Alexey Belkov, Commented Feb 11, 2021 at 12:30

Xavier Guihot · Accepted Answer · 2021-08-27 07:08:00Z

32

You have to put all Java classes under src/main/java, instead of src/main/kotlin.

Just right click on main -> new -> directory -> select java (or type it).

edited Aug 27, 2021 at 7:08

Xavier Guihot

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answered Aug 27, 2021 at 6:58

APTower

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Mehranjp73 Over a year ago

You are a lifesaver.

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