Call Function From Another Class In Main Using Flutter

import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class Second {
  void randomMSG() {
    print('Second Class Function Called.');
  }
  void printText(String holder) {
    print(holder);
  }
  double returnMSG(double a, double b){
    double number ;
    number = a + b ;
    return number ;
  }
}
class MyApp extends StatelessWidget {
  final second = Second();
  void fn_1() {
    second.randomMSG();
  }
  void fn_2() {
    second.printText('Function With Argument Called');
  }
  void fn_3(){
    double holder ;
    holder = second.returnMSG(12, 13);
    print(holder);
  }
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
        home: Scaffold(
            body: Center(
                child: Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: <Widget>[
                      Container(
                          margin: const EdgeInsets.fromLTRB(20, 10, 20, 10),
                          child:
                          RaisedButton(
                            onPressed: () => fn_1(),
                            child: Text('Call Another Class Function Without Argument',
                              textAlign: TextAlign.center,),
                            textColor: Colors.white,
                            color: Colors.indigo,
                            padding: EdgeInsets.fromLTRB(12, 12, 12, 12),
                          )
                      ),
                      Container(
                          margin: const EdgeInsets.fromLTRB(20, 10, 20, 10),
                          child:
                          RaisedButton(
                            onPressed: () => fn_2(),
                            child: Text('Call Another Class Function With Argument',
                                textAlign: TextAlign.center),
                            textColor: Colors.white,
                            color: Colors.indigo[300],
                            padding: EdgeInsets.fromLTRB(12, 12, 12, 12),
                          )
                      ),
                      Container(
                          margin: const EdgeInsets.fromLTRB(20, 10, 20, 10),
                          child:
                          RaisedButton(
                            onPressed: () => fn_3(),
                            child: Text('Call Another Class Function With Return Value',
                                textAlign: TextAlign.center),
                            textColor: Colors.white,
                            color: Colors.indigo,
                            padding: EdgeInsets.fromLTRB(12, 12, 12, 12),
                          )
                      ),
                    ])
            )
        )
    );
  }
}