what’s the core difference between statelesswidget and statefulwidget?

In the broadest possible sense, the state of an app is everything that exists in memory when the app is running . This includes the app’s assets, all the variables that the Flutter framework keeps about the UI, animation state, textures, fonts, and so on.

Widgets are the central class hierarchy in the Flutter framework . A widget is an immutable description of part of a user interface. Widgets can be inflated into elements, which manage the underlying render tree. Widgets themselves have no mutable state (all their fields must be final).

The runApp() function takes the given Widget and makes it the root of the widget tree . In this example, the widget tree consists of two widgets, the Center widget and its child, the Text widget. The framework forces the root widget to cover the screen, which means the text “Hello, world” ends up centered on screen.