java 不知道这是什么意思

如果在Class Path选中d8就会出现下图这种

如果不选中d8就会说找不到主类什么的

代码
//FileName:MyWindow.java
import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.control.Button;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.Pane;
import javafx.geometry.Insets;
public class MyWindow extends Application{
@Override
public void start(Stage primaryStage){
BorderPane rootPane=new BorderPane( );
rootPane.setPadding(new Insets(8,8,8,8));
Image imb=new Image("国旗.jpg");
ImageView iv=new ImageView(imb);
iv.setFitWidth(80);
iv.setPreserveRatio(true);
iv.setSmooth(true);
iv.setCache(true);
Pane pane=new Pane( );
pane.getChildren( ).add(iv);
Button bt=new Button("北部区域");
rootPane.setTop(bt);
rootPane.setBottom(new Button("南部区域"));
rootPane.setLeft(new Button("西部区域"));
rootPane.setRight(new Button("显示信息"));
rootPane.setCenter(pane);
Scene scene=new Scene(rootPane);
primaryStage.setTitle("界面布局");
primaryStage.setScene(scene);
primaryStage.show( );
}
}

代码贴出来