Flutter Create Call Function From Same Class On Click Button

import 'package:flutter/material.dart';

void main(){
  runApp(MyApp());
}

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 {
  void sampleFunction_1() {
    print('Function Called');
  }

  void sampleFunction_2(String holder) {
    print(holder);
  }

  void sampleFunction_3(double value){
    print(value);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.red[900],
        title: Text('Call Function From Same Class'),
      ),
            body: Center(
                child: Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: <Widget>[

                      Container(
                          child: RaisedButton(
                            onPressed: () => sampleFunction_1(),
                            child: Text(' Function Without Argument '),
                            textColor: Colors.white,
                            color: Colors.red[900],
                          )
                      ),

                      Container(
                          child: RaisedButton(
                            onPressed: () => sampleFunction_2('Hello Word'),
                            child: Text(' Function With String Argument '),
                            textColor: Colors.white,
                            color: Colors.red[400],
                          )
                      ),

                      Container(
                          child: RaisedButton(
                            onPressed: () => sampleFunction_3(145.123),
                            child: Text(' Function With Double Float Argument '),
                            textColor: Colors.white,
                            color: Colors.red[900],
                          )
                      )

                    ])
            )
    );
  }
}