So you upgraded an existing project to a newer version?

Nope i created a new project using cocos2dx 3.15 and then copied classes and resources file and then imported share and appodeal plugin.

I used to compile using cocos console but since i had to use multidex, as i needed facebook and appodeal plugin both , i had to switch to androdi studio.

So now i am compiling using android studio..and it gives this error..

I just found this one post with same error : but with different entry and this is the solution mentioned. – http://discuss.cocos2d-x.org/t/solved-post-facebook-integration-issue-cocos-compile-failed/29931/14?u=mihir77

I had done 2 and 3 points but in first point..

1. updated my Application class:

public class App extends Application {
  @Override
  protected void attachBaseContext(Context base) {
    super.attachBaseContext(base);
    MultiDex.install(this);
 }
}

I cannot find the application class and if i have to create how and where?

Did the new project work without adding the extra files?

Yes it works without adding share plugin and multidex.

Does cocos helper plugins – facebook and twitter share supoort cocos2dx 3.15.

Should i use that instead of sdkbox share?

Yes Cocos Helper does. I would use it over SDKBOX.