Flutter 无状态Hello world程序

Flutter 无状态Hello world程序：

import 'package:flutter/material.dart';


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

class MyApp extends StatelessWidget{
  @override
  Widget build(BuildContext context) {
   return MaterialApp(title: "hello world",home: new MyHomePage(),);
  }
  
}

class MyHomePage extends StatelessWidget{
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("AppBar title")),
      body: Center(child: Text('Hello world'),),);
  }
  
}