How to use setOnAction event on javafx - javafx

Question

I would like to validate if a textfield is empty or not using javafx.
I am confused of event handlers. I want to confirm :
- whether there are many ways to use setOnAction :
submit.setOnAction((new EventHandler<MouseEvent>() {
public void handle(MouseEvent event) {
System.out.println("Hello World");
}
}));
or
submit.setOnAction(e -> handle(e));
what is the difference between these two choices?
whether the second choice can not use the ActionEvent
submit.setOnAction(e -> handle());
but then what is the purpose of defining e?
I would like to validate textfields in my application.
public class AppGUI extends Application{
public static void main(String[] args)
{
launch();
}
public void start(Stage topView)
{
createUI(topView);
}
private void createUI(Stage topView)
{
TextField name = TextField();
Button submit = new Button("Submit");
submit.setOnAction(e -> validate());
}
private boolean validate()
{
// if textfield is empty, return false. else, return true.
}
I am lost here. Is it okay if the e in setOnAction is not used in validate? How do I pass the value of textfield to validate()? is making the textfields private variables the only way? (because I have so many text fields I wonder if its a good option).
in createUI method, how do i say if validate() returns false, show error message and if true, do something else?
Thank you and sorry for bothering

Answer 1

what is the difference between these two choices?
In second option lambdas are used (appeared since Java 8)
but then what is the purpose of defining e?
For a button your method have a signature like this setOnAction(EventHandler<ActionEvent> handler) You should see EventHandler tutorials and an ActionEvent javadoc. For instance, from e you can get the object on which the Event initially occurred this way e.getSource()
It is ok if you don't use e in validate.
To pass the value of textfield your method should have signature like this
boolean validate(String text);
Code example:
private void createUI(Stage topView){
TextField name = TextField();
Button submit = new Button("Submit");
submit.setOnAction(e -> {
boolean validated = validate(name.getText());
if(validated) System.out.println("validated");
}
}
private boolean validate(String text){
return text != null && !text.isEmpty();
}