Multi tool use

Clash Royale CLAN TAG

setOnAction restrictions and datepicker class

I'm writing an application involved in time difference, there is something I don't get it,

final DatePicker datePick=new DatePicker();
LocalDate time;
Label label=new Label();
datePick.setOnAction(new EventHandler<ActionEvent>(){
public void handle(ActionEvent e){
time=datePick.getValue();//doesn't work, must 'LocalDate time=datePick.getValue();
label.setText(time);//doesn't work must label.setText("Time now:"+time)
}
});


It gives an error saying "Local variables referenced from an inner class must be final or effectively fine", anyway, all I did, declare 'time' variable inside setOnAction() and it worked, so what was wrong? and 'label.setText(time);' if I don't write some text inside, like 'label.setText("Time now: "+ time);' ,won't work too, that's weird, yet why?

label.setText(datePicekr.getValue());

1 Answer
1

Java restricts local variables you access from a anonymus class/lambda expression to those that never change their values after assignment (i.e. thoser the compiler wouldn't complain about, if you declared them as final). If you could write to the local variable from a anonymus class this would violate this condition. It's not possible to write to local variables of the containing method from anonymus classes for this reason.

final

You should declare variables in the scope where they are needed anyways.

As for label.setText(time);:

label.setText(time);

Label.setText is a method with a String parameter. Since String is not a supertype of LocalDate, a simple assignment won't work. You need to convert the date to a String. String concatenation does this automatically, i.e. the + operator receiving a String s as first operand and a Object o as second operand outputs the concatenation of s and Objects.toString(o).

Label.setText

String

String

LocalDate

String

+

String s

Object o

s

Objects.toString(o)

You could simply invoke toString yourself:

toString

label.setText(time.toString());


Or use a more sophisticated method for convertion to string.

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