How To Create Abstract Class Methods Using Flutter Dart

import 'package:flutter/material.dart';
void main() => runApp(MyApp());
abstract class Message{
  void run();
  void fun();
}

class Second extends Message {
  void run(){
    print('Run Fast......');
  }
  void fun(){
    print('Have Fun......');
  }

}
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.red[800],
          title: Text('Abstract Class Methods'),
        ),
        body: Center(
            child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  Container(
                      child: RaisedButton(
                        onPressed: () => second.fun(),
                        child: Text('Call Abstract Class Fun Function',
                          textAlign: TextAlign.center,),
                        textColor: Colors.white,
                        color: Colors.red,
                      )
                  ),

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