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Why can't I run Main.java on Eclipse "Errors exist in required project(s)"

Here is error when I press run:
Down is Main.java and I don't know what this is. Yesterday I used this file and nothing happened.
package application;
import javafx.application.Application;
import javafx.stage.Stage;
import javafx.stage.StageStyle;
import javafx.scene.Scene;
import javafx.scene.image.Image;
import javafx.scene.layout.BorderPane;
import javafx.fxml.FXMLLoader;
public class Main extends Application {
#Override
public void start(Stage primaryStage) {
try {
BorderPane root = (BorderPane)FXMLLoader.load(getClass().getResource("LogIn.fxml"));
Scene scene = new Scene(root, 700,512);
scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
primaryStage.initStyle(StageStyle.DECORATED);
primaryStage.setScene(scene);
primaryStage.show();
primaryStage.setTitle("Log In");
Image icon = new Image(getClass().getResourceAsStream("sherr.jpeg"));
primaryStage.getIcons().add(icon);
primaryStage.setResizable(false);
} catch(Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
launch(args);
}
}
Here is what displayed on Console

Java FX 'cannot find symbol'

I'm new to java and java fx, I am trying to create a simple window but I keep getting the error
java: cannot find symbol
symbol: class Group
location: class sample.Main
This is my code:
package sample;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
public class Main extends Application {
public static void main(String[] args) {
launch(args);
}
#Override
public void start(Stage primaryStage) throws Exception{
Group root = new Group();
Scene scene = new Scene(root);
primaryStage.setScene(scene);
primaryStage.show();
}
}

You aren't importing javafx.scene.Group. Add
import javafx.scene.Group;

Cannot change the width of a button below a certain minimum

I have this code:
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.ToggleButton;
import javafx.scene.image.Image;
import javafx.scene.layout.Background;
import javafx.scene.layout.BackgroundImage;
import javafx.scene.layout.BackgroundSize;
import javafx.scene.layout.TilePane;
import javafx.stage.Stage;
public class ToggleButtonSize extends Application {
#Override
public void start(Stage stage) throws Exception {
var toggleButton = new ToggleButton();
toggleButton.setMaxHeight(10);
toggleButton.setMaxWidth(10);
// tried also
toggleButton.setStyle("-fx-max-width: 10; -fx-pref-width: 10;");
var pane = new FlowPane(toggleButton);
var scene = new Scene(pane);
stage.setScene(scene);
stage.show();
}
public static void main(String[] args) {
launch(args);
}
}
This code works fine, but when I use MobileApplication instead the minimum width does not go to 10:
How can I shrink the size like when using Application?

Swap JavaFX scene when clicking a button

I am trying to create a program to teach people about GNU/Linux and the command line, I have my main.java
package sample;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;
public class Main extends Application {
Stage window;
public static void main(String[] args) {
launch(args);
}
#Override
public void start(Stage primaryStage) throws Exception {
window = primaryStage;
Parent root = FXMLLoader.load(getClass().getResource("login.fxml"));
primaryStage.setTitle("Learnix");
primaryStage.setScene(new Scene(root, 800, 500));
primaryStage.show();
}
}
And the controller to go with it.
package sample;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import java.io.IOException;
public class loginController {
public Button loginBtn;
public void loginBtnClick() throws IOException {
System.out.println("You are logged in");
}
}
I have tried things such as:
FXMLLoader.load(getClass().getResource("lessons.fxml"));
But I can't figure out how to get it to swap scenes. I have seen many tutorials on YouTube and it Stack Overflow but many of them have all of the JavaFX on the main.java and not in separate files as I am using scenebuilder.
Thank you.

You can either call Stage.setScene() to change the whole scene or just substitute a root to the new one by Scene.setRoot():
Parent newRoot = FXMLLoader.load(getClass().getResource("lessons.fxml"));
primaryStage.getScene().setRoot(newRoot);

BorderPane is hiding bottom region until window is maximized

BorderPane in JavaFx application does not show bottom region Node unless the window is maximized when the scene is switched using Button event. If the scenes are switched one after another its arranged perfectly. Do I have bugs in my code or is this the default behaviour? Thanks.
System : Windows XP
Java version : 7
My SSCE:
import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.geometry.Pos;
import javafx.geometry.Rectangle2D;
import javafx.stage.Screen;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
public class Main extends Application {
#Override
public void start(final Stage stage) {
try {
///// 2nd scene
BorderPane root2 = new BorderPane();
root2.setPrefSize(stage.getWidth(),stage.getHeight());
HBox buttons2=new HBox(50);
buttons2.getChildren().addAll(new Button("Button1"),new Button("Button2"));
buttons2.setAlignment(Pos.BOTTOM_CENTER);
root2.setBottom(buttons2);
final Scene scene2 = new Scene(root2,stage.getWidth(),stage.getHeight());
///// 1st scene
VBox buttons1=new VBox();
buttons1.setPrefSize(stage.getWidth(),stage.getHeight());
Button nextSceneBtn=new Button("NEXT");
buttons1.getChildren().add(nextSceneBtn);
buttons1.setAlignment(Pos.CENTER);
Scene scene1=new Scene(buttons1,stage.getWidth(),stage.getHeight());
////action event
nextSceneBtn.setOnMouseClicked(new EventHandler<MouseEvent>(){
#Override
public void handle(MouseEvent event) {
stage.setScene(scene2);
}
});
///stage
Screen screen = Screen.getPrimary();
Rectangle2D bounds = screen.getVisualBounds();
stage.setX(0);
stage.setY(0);
stage.setWidth(bounds.getWidth());
stage.setHeight(bounds.getHeight());
stage.setScene(scene1); //if it's #setScene(scene2) at the beginning, it's ok
stage.show();
} catch(Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
launch(args);
}
}

That looks like a bug, which seems to have been fixed in JavaFX 8. Obviously if you're running on Windows XP, that's of limited use.
A possible workaround is to switch the root of the scene, instead of the scene itself:
import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.geometry.Pos;
import javafx.geometry.Rectangle2D;
import javafx.stage.Screen;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
public class Main extends Application {
#Override
public void start(final Stage stage) {
try {
///// 2nd scene
final BorderPane root2 = new BorderPane();
root2.setPrefSize(stage.getWidth(),stage.getHeight());
HBox buttons2=new HBox(50);
buttons2.getChildren().addAll(new Button("Button1"),new Button("Button2"));
buttons2.setAlignment(Pos.BOTTOM_CENTER);
root2.setBottom(buttons2);
// final Scene scene2 = new Scene(root2,stage.getWidth(),stage.getHeight());
///// 1st scene
VBox buttons1=new VBox();
buttons1.setPrefSize(stage.getWidth(),stage.getHeight());
Button nextSceneBtn=new Button("NEXT");
buttons1.getChildren().add(nextSceneBtn);
buttons1.setAlignment(Pos.CENTER);
final Scene scene1=new Scene(buttons1,stage.getWidth(),stage.getHeight());
////action event
nextSceneBtn.setOnMouseClicked(new EventHandler<MouseEvent>(){
#Override
public void handle(MouseEvent event) {
// stage.setScene(scene2);
scene1.setRoot(root2);
}
});
///stage
Screen screen = Screen.getPrimary();
Rectangle2D bounds = screen.getVisualBounds();
stage.setX(0);
stage.setY(0);
stage.setWidth(bounds.getWidth());
stage.setHeight(bounds.getHeight());
stage.setScene(scene1); //if it's #setScene(scene2) at the beginning, it's ok
stage.show();
} catch(Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
launch(args);
}
}