cannot load application.Main

cannot get my environment for the new JavaFX 11 right on Eclipse

package application;

import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.layout.StackPane;


public class Main extends Application {
    @Override
    public void start(Stage primaryStage) {
        String javaVersion = System.getProperty("java.version");
        String javafxVersion = System.getProperty("javafx.version");
        Label l = new Label("Hello, JavaFX " + javafxVersion + ", running on Java " + javaVersion + ".");
        Scene scene = new Scene(new StackPane(l), 640, 480);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch();
    }
}

错误: 找不到或无法加载主类 application.Main 原因: java.lang.NoClassDefFoundError: javafx/application/Application

that's the console result,the code won't give error,the problem is that it couldn't run.