What does Underscore "_" before variable name mean for Flutter

Question

with reference to the Flutter tutorial, I encountered an underscore, _.

I know that in Java, _ is used as a naming convention for a private variable.

1. Does it also apply to Flutter? Noting that there is no public/protected in Flutter.
2. Will the _ really be private (inaccessible by other classes) or is it just a naming convention?

Variable

class RandomWordsState extends State<RandomWords> {   final List<WordPair> _suggestions = <WordPair>[];   final Set<WordPair> _saved = new Set<WordPair>();   final TextStyle _biggerFont = const TextStyle(fontSize: 18.0);   ... } 

3. Does the _ make the Widget private too? In this case, wouldn't the main class be unable to assess the Widget?

Function

Widget _buildRow(WordPair pair) {   final bool alreadySaved = _saved.contains(pair);  // Add this line.   ... } 

Answer 1

It's not just a naming convention. Underscore fields, classes and methods will only be available in the .dart file where they are defined.

It is common practice to make the State implementation of a widget private, so that it can only be instantiated by the corresponding StatefulWidget:

class MyPage extends StatefulWidget {   @override   _MyPageState createState() => _MyPageState(); }  class _MyPageState extends State<MyPage> {   @override   Widget build(BuildContext context) {     return Container();   } }