on this app have the option for practice interface design? like joptionpane, fx, etc

Answer 1

No, the Code Playground of this app only allows you to do console applications.

Answer 2

With that app, you can only write everything in one place.

Answer 3

thanks another question, to work with classes I just can create class in the same "file"? for example if I need to create a class I can create another file just for that class? or only is possible to write on the same place of main (like NetBeans)