interface OnResponseCallback {
    void onResponse(int[] data);
}

class MainActivity implements OnResponseCallback {
    public MainActivity() {
        Response response = new Response(this);

    }

    @Override
    public void onResponse(int[] data) {
        //Обработка полученных данных
    }
}

class Response {
    OnResponseCallback mOnResponseComplete;
    public Response(OnResponseCallback onResponseComplete) {
        mOnResponseComplete = onResponseComplete;
        returnDataToMainActivity();
    }

    void returnDataToMainActivity() {
        mOnResponseComplete.onResponse(new int[] {1, 2, 3});
    }
}