how to start an activity in another module explicitly

Intent intent = new Intent();
intent.setClassName(context.getPackageName(), "ir.sibvas.testlibary1.HelloWorldActivity");
startActivity(intent);

You can use the Class.forName(), it worked for me when i was needed to start activity which is in another module in my project.

 Intent intent = null;
    try {
        intent = new Intent(this, 
           Class.forName("ir.sibvas.testlibary1.HelloWorldActivity"));
        startActivity(intent);
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }

First module activity launch then second module activity launch and write a line of code is perfectly fine.

try {
  Intent launchIntent =
      getPackageManager().getLaunchIntentForPackage("com.your.packagename");
  if (launchIntent != null) {
    startActivity(
        launchIntent); //null pointer check in case package name was not found ClassNotFoundException
  }
} catch (e) {
  e.printStackTrace();
}