Problem with JavaFX ChangeListener?

[Knute Johnson]

I'm trying to teach myself JavaFX and have hit a snag. In the program
below I add a ChangeListener to a TextField. The Java8 method works
fine, adding an anonymous ChangeListener class works fine but I can't
create a class that implements ChangeListener and get it to compile.

The other question I have is why does the ObservableValue require a cast
to StringProperty in both of the working examples and why do I declare
it as <? extends String>?

Thanks,

knute...

import javafx.application.*;
import javafx.beans.*;
import javafx.beans.property.*;
import javafx.beans.value.*;
import javafx.event.*;
import javafx.scene.*;
import javafx.scene.control.*;
import javafx.scene.layout.*;
import javafx.stage.*;

import java.time.*;

public class test99 extends Application {
public static void main(String... args) {
launch(args);
}

public void start(Stage primaryStage) {
primaryStage.setTitle("test99");
VBox root = new VBox(10);
Scene scene = new Scene(root,320,240);

TextField textField = new TextField();
textField.setOnAction(ae ->
System.out.println(textField.getText()));

textField.textProperty().addListener((observable,oldValue,newValue) -> {
((StringProperty)observable).setValue(newValue.toLowerCase());
});

/*
class LengthListener<String> implements ChangeListener<String> {
private final int length;

public LengthListener(int length) {
this.length = length;
}

@Override public void changed(
ObservableValue<? extends String> observable,
String oldValue,String newValue) {
if (newValue.length() > length)
((StringProperty)observable).setValue(
newValue.substring(0,length));
}
}
textField.textProperty().addListener(new LengthListener(4));
*/


textField.textProperty().addListener((observable,oldValue,newValue) -> {
((StringProperty)observable).setValue(newValue.length() > 4 ?
newValue.substring(0,4) : newValue);
});

/*
textField.textProperty().addListener(new ChangeListener<String>() {
@Override
public void changed(ObservableValue<? extends String>
observable,
String oldValue,String newValue) {
((StringProperty)observable).setValue(newValue.length()
> 4 ?
newValue.substring(0,4) : newValue);
}
});
*/

textField.setText("Hello World!");

root.getChildren().add(textField);
primaryStage.setScene(scene);
primaryStage.show();
}
}


--

Knute Johnson

[Arne Vajhøj]

On 12/11/2014 6:08 PM, Knute Johnson wrote:
> I'm trying to teach myself JavaFX and have hit a snag. In the program
> below I add a ChangeListener to a TextField. The Java8 method works
> fine, adding an anonymous ChangeListener class works fine but I can't
> create a class that implements ChangeListener and get it to compile.

> class LengthListener<String> implements ChangeListener<String> {

^^^^^^^^ remove this (it has a very bad
impact when String is used later!)

> private final int length;
>
> public LengthListener(int length) {
> this.length = length;
> }
>
> @Override public void changed(
> ObservableValue<? extends String> observable,
> String oldValue,String newValue) {
> if (newValue.length() > length)
> ((StringProperty)observable).setValue(
> newValue.substring(0,length));
> }
> }
> textField.textProperty().addListener(new LengthListener(4));

Arne

[Knute Johnson]

Thanks Arne, that was why it wouldn't compile!

--

Knute Johnson

[Arne Vajhøj]

On 12/11/2014 6:08 PM, Knute Johnson wrote:

> The other question I have is why does the ObservableValue require a cast
> to StringProperty in both of the working examples and why do I declare
> it as <? extends String>?

> class LengthListener<String> implements ChangeListener<String> {
> private final int length;
>
> public LengthListener(int length) {
> this.length = length;
> }
>
> @Override public void changed(
> ObservableValue<? extends String> observable,
> String oldValue,String newValue) {
> if (newValue.length() > length)
> ((StringProperty)observable).setValue(
> newValue.substring(0,length));
> }
> }
> textField.textProperty().addListener(new LengthListener(4));

Formal type of observable:

interface javafx.beans.value.ObservableValue

Actual ype of observable:

class javafx.scene.control.TextInputControl$TextProperty
**** class javafx.beans.property.StringProperty
******** interface javafx.beans.value.ObservableValue

The cast is necessary!

Arne

[Knute Johnson]

OK, I see now. Thanks for that too Arne.

--

Knute Johnson

[Roedy Green]

On Thu, 11 Dec 2014 15:08:08 -0800, Knute Johnson
<ete...@knutejohnson.com> wrote, quoted or indirectly quoted someone
who said :

> class LengthListener<String> implements ChangeListener<String> {

Look at the code for ChangeListener

public interface ChangeListener extends EventListener

There is no <xxxx>. You can't just make one up.

--
Roedy Green Canadian Mind Products http://mindprod.com
Software is a gas; it expands to fill its container.
~ Nathan Myhrvold (born: 1959-08-03 age: 55) Nathan’s First Law

[Joerg Meier]

On Wed, 31 Dec 2014 18:23:33 -0800, Roedy Green wrote:

> On Thu, 11 Dec 2014 15:08:08 -0800, Knute Johnson
> <ete...@knutejohnson.com> wrote, quoted or indirectly quoted someone
> who said :
>> class LengthListener<String> implements ChangeListener<String> {
> Look at the code for ChangeListener

> public interface ChangeListener extends EventListener

> There is no <xxxx>. You can't just make one up.

javax.swing.event.ChangeListener

is not the same as

javafx.beans.value.ChangeListener

the latter is defined as

public interface ChangeListener<T>

This is a good example of why using * imports is a bad idea. I recommend
getting a modern IDE to prevent such issues.

Liebe Gruesse,
Joerg

--
Ich lese meine Emails nicht, replies to Email bleiben also leider
ungelesen.