java.lang.IllegalStateException: Dex archives: setting .DEX extension only for .CLASS files

./gradlew clean fixed the same error for me.

For Cordova developers,

If you get this build error in your project, as said Pierrick Martellière in the comments of this answer, in you project folder use :

cordova clean

It makes a cleaning and a build immediately

It seems I found the solution. At the build moment gradle was showing warnings for me:

Configuration 'compile' in project ':app' is deprecated. Use 'implementation' instead.

app: 'androidProcessor' dependencies won't be recognized as kapt annotation processors. Please change the configuration name to 'kapt' for these artifacts: 'com.arello-mobile:moxy-compiler:1.5.3' and apply the kapt plugin: "apply plugin: 'kotlin-kapt'".

I made a misspelling and forgot to remove unnecessary annotationProcessor for library:

annotationProcessor "com.arello-mobile:moxy-compiler:$moxyVersion"
kapt "com.arello-mobile:moxy-compiler:$moxyVersion"

So I removed first line.

After that I applied kapt plugin apply plugin: 'kotlin-kapt' and fixed some build errors in code after it.

After all I realized that I forgot to replace compile to implementation in some places. It is weird but without it build didn't work.

This changes fix my error build.

Simple Solution

For Ionic and Cordove Projects

cordova clean

Above answer is mostly right but in my case, i get this exception when i crate same name java and kotlin file then deletes one of them.

Solutions are: just Build -> Clean Project my project and it works. And my project also enabled multiDex.

defaultConfig {
        ...
        // Enabling multidex support.
        multiDexEnabled true
    }