Question

I have a virtual machine running Windows XP SP3 32-bit. On this machine
I installed the Java SE JDK 8 build b44 Developer Preview from here.

I also installed the JavaFX 2.1 SDK.

It works fine:

java -version
> java version "1.8.0-ea"
> Java(TM) SE Runtime Environment (build 1.8.0-ea-b44)
> Java HotSpot(TM) Client VM (build 24.0-b14, mixed mode, sharing)

I tried running the following program (taken from here):

import javafx.application.Application;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.ButtonBase;
import javafx.scene.control.ToggleButton;
import javafx.scene.control.ToggleButtonBuilder;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;

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

    @Override  public void start(Stage stage) throws Exception
    {
        BorderPane root = new BorderPane();
        ToggleButton button = new ToggleButton("Click");
        final StringProperty btnText = button.textProperty();

        button.setOnAction(new EventHandler<ActionEvent>()
        {
            @Override public void handle(ActionEvent actionEvent)
            {
                ToggleButton source = (ToggleButton) actionEvent.getSource();
                if (source.isSelected())
                {
                    btnText.set("Clicked!");
                }
                else
                {
                    btnText.set("Click!");
                }
            }
        });

        root.setCenter(button);
        Scene scene = new Scene(root);
        stage.setScene(scene);
        stage.setWidth(200);
        stage.setHeight(200);
        stage.show();
    }
}

The program compiled and ran as expected.

I followed the instructions in that article and replaced the button event-handling code with this:

button.setOnAction((ActionEvent event)->
{
    ToggleButton source = (ToggleButton) event.getSource();
    if (source.isSelected())
    {
        btnText.set("Clicked!");
    }
    else
    {
        btnText.set("Click!");
    }
});

When compiling, I get the following error (on the line button.setOnAction((ActionEvent event)->):

> lambda expressions are not supported in -source 1.8
> (use -source 8 or higher to enable lambda expressions)

I added the argument -source 8, nothing changed.

All I wanted was to check the lambda expressions functionality in Java 8. Why doesn’t it work ?

Answer 1

You need to download the binaries which contain the Lambda expressions feature. Try downloading from here http://jdk8.java.net/lambda/.
I remember reading in the mailing list that the lambda expression branch is being merged in the main JDK8 build, but not sure if its been done. But I use the build from the Lambda project page.