ความแตกต่างระหว่าง StatelessWidget และ StatefulWidget คืออะไร?

// a StatelessWidget: just describes UI based on its inputs (immutable, no internal state)
class Greeting extends StatelessWidget {
  final String name;
  const Greeting(this.name);

  @override
  Widget build(BuildContext context) {
    return Text('Hello, $name');   // UI depends only on inputs, never changes itself
  }
}
// → use for UI that doesn't change on its own (static content, displays based on inputs)