Lambda表达式在Java 8中不起作用？

Question

我有一台运行Windows XP SP3 32位的虚拟机.在这台机器上,我从这里安装了Java SE JDK 8 build b44 Developer Preview .

我还安装了JavaFX 2.1 SDK.

它工作正常:

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)

我尝试运行以下程序(取自此处):

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();
    }
}

该程序按预期编译和运行.

我按照那篇文章中的说明操作,并将按钮事件处理代码替换为:

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

编译时,我得到以下错误(在线button.setOnAction((ActionEvent event)->):

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

我补充说-source 8,没有改变.

我想要的只是检查Java 8中的lambda表达式功能.为什么它不起作用？

Answer 1

您需要下载包含Lambda表达式功能的二进制文件.尝试从这里下载http://jdk8.java.net/lambda/.我记得在邮件列表中读到lambda表达式分支正在主JDK8构建中合并,但不确定它是否已完成.但我使用Lambda项目页面中的构建.