Abstract Class Can Not Be Instantiated Using Flutter Android

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

abstract class Message{
  void Hello();
  void By();
}
class Second extends Message {
  void Hello(){
    print('Hello Guys Welcome To BajarangiSoft...');
  }
  void By(){
    print('By Guys...');
  }

}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: MyHomePage(),
    );
  }
}
class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with SingleTickerProviderStateMixin {
  final second = new Second();
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      appBar: AppBar(
        backgroundColor: Colors.pink[600],
        title: Text('Abstract Class'),
      ),
            body: Center(
                child: Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: <Widget>[

                      Container(
                          child: RaisedButton(
                            onPressed: () => second.Hello(),
                            child: Text('Call Abstract Class Hello Function',
                              textAlign: TextAlign.center,),
                            textColor: Colors.white,
                            color: Colors.pink,
                          )
                      ),

                      Container(
                          child: RaisedButton(
                            onPressed: () => second.By(),
                            child: Text('Call Abstract Class By Function',
                                textAlign: TextAlign.center),
                            textColor: Colors.white,
                            color: Colors.pink[600],
                          )
                      ),
                    ])
            )
    );
  }
}