Display JSON data in Flutter : Using the main() function

LoadJson1.dart

import 'package:flutter/material.dart';
import 'dart:convert';
import 'dart:async' show Future;
import 'package:flutter/services.dart' show rootBundle;

class Student {
  String studentId;
  String studentName;
  int studentScores;
  Student({this.studentId, this.studentName, this.studentScores});
  factory Student.fromJson(Map<String, dynamic> parsedJson) {
    return Student(
        studentId: parsedJson['id'],
        studentName: parsedJson['name'],
        studentScores: parsedJson['score']);
  }
}

Future<String> _loadAStudentAsset() async {
  return await rootBundle.loadString('assets/student.json');
}

Future<Student> loadStudent() async {
  String jsonString = await _loadAStudentAsset();
  final jsonResponse = json.decode(jsonString);
  return new Student.fromJson(jsonResponse);
}

void main() async {
  Student student = await loadStudent();
  runApp(MyApp(student: student));
}

class MyApp extends StatefulWidget {
  final Student student;
  MyApp({this.student});
  @override
  MyAppState createState() => MyAppState();
}

class MyAppState extends State<MyApp> {
  @override
  void initState() {
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new Scaffold(
          appBar: new AppBar(
            title: new Text('Load Json'),
          ),
          body: new Container(
              padding: new EdgeInsets.all(20.0),
              child: new Row(
                children: <Widget>[
                  Text(
                      "Hi ${widget.student.studentName} your id is ${widget.student.studentId} and score ${widget.student.studentScores} ")
                ],
              ))),
    );
  }
}

where is the json file ?