main.dart
import 'package:flutter/material.dart';
​
void main() {
  runApp(
    new Center(
      child: new Text(
        'Hello, world!'
      ),
    ),
  );
}

import 'package:flutter/material.dart';
​
void main() {
  runApp(
    new MaterialApp(
      title: 'Hello World App',
      home: new myApp(),
    )
  );
}
​
class myApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Hello World App'),
      ),
      body: new Center(
        child: new Text(
          'Hello, world!'
        ),
      ),
    );
  }
}