javafx fxml program error(no main method)

问题

i'm fairly new to javafx and fxml. I'm trying to teach myself! However, when I was creating a program for a simple login GUI I came into an issue when I finally tried to run my program. It told me there was no main method in my class and I'm unsure of how to fix it. Any ideas?

My program creates a login screen and when you enter "test" for the username and password it'll take you to another scene.

Here is my Login.java

package com;

    import javafx.application.Application;
    import javafx.fxml.FXMLLoader;
    import javafx.stage.Stage;
    import javafx.scene.Parent;
    import javafx.scene.Scene;

    /**
     *
     * @author Tyler
     */
    public class Login extends Application{

        @Override
        public void start(Stage stage) throws Exception {
            Parent root = FXMLLoader.load(getClass().getResource("Login.fxml"));
            Scene scene = new Scene(root);
            stage.setScene(scene);
            stage.setTitle("Login");
            stage.show();
        }

    }

Here is my LoginController.java

package com;

import java.net.URL;
import java.util.ResourceBundle;
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.scene.Node;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.PasswordField;
import javafx.scene.control.TextField;
import javafx.stage.Stage;

/**
 * FXML Controller class
 *
 * @author Tyler
 */
public class LoginController implements Initializable {

    @FXML
    private Label lblMessage; 
    @FXML
    private TextField txtUsername;
    @FXML
    private PasswordField txtPassword;
    @FXML
    private void btnLoginAction(ActionEvent event) throws Exception{
        if(txtUsername.getText().equals("test") && txtPassword.getText().equals("test")){
            ((Node) (event.getSource())).getScene().getWindow().hide();
            Parent parent = FXMLLoader.load(getClass().getResource("DateSelection.fxml"));
            Stage stage  = new Stage();
            Scene scene = new Scene(parent);
            stage.setScene(scene);
            stage.setTitle("Date Selection");
            stage.show();
        }else{
            lblMessage.setText("Username or Password is invalid!");
        }
    }
    /**
     * Initializes the controller class.
     * @param url
     * @param rb
     */
    @Override
    public void initialize(URL url, ResourceBundle rb) {
        // TODO
    }    

}

Here is my Login.fxml

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.text.*?>
<?import java.lang.*?>
<?import java.util.*?>
<?import javafx.scene.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>

<AnchorPane id="AnchorPane" fx:id="lblMessage" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="com.LoginController">
   <children>
      <PasswordField fx:id="txtPassword" layoutX="200.0" layoutY="200.0" prefHeight="30.0" prefWidth="200.0" promptText="Password" />
      <TextField fx:id="txtUsername" layoutX="200.0" layoutY="140.0" prefHeight="30.0" prefWidth="200.0" promptText="Username" />
      <Button fx:id="btnLogin" layoutX="269.0" layoutY="251.0" mnemonicParsing="false" onAction="#btnLoginAction" prefHeight="30.0" text="Login">
         <font>
            <Font size="14.0" />
         </font></Button>
      <Label fx:id="lblMessage" layoutX="283.0" layoutY="71.0" text="Label" />
   </children>
</AnchorPane>

Here is my DateSelectionController.java

package com;

import java.net.URL;
import java.util.ResourceBundle;
import javafx.fxml.Initializable;

/**
 * FXML Controller class
 *
 * @author Tyler
 */
public class DateSelectionController implements Initializable {

    /**
     * Initializes the controller class.
     */
    @Override
    public void initialize(URL url, ResourceBundle rb) {
        // TODO
    }    

}

Here is my DateSelection.fxml

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.text.*?>
<?import java.lang.*?>
<?import java.util.*?>
<?import javafx.scene.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>


<AnchorPane id="AnchorPane" prefHeight="400.0" prefWidth="600.0" xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/8" fx:controller="com.DateSelectionController">
   <children>
      <Label layoutX="191.0" layoutY="164.0" text="Welcome">
         <font>
            <Font name="System Bold" size="50.0" />
         </font>
      </Label>
   </children>
</AnchorPane>

回答1:

From Oracle:

The main() method is not required for JavaFX applications when the JAR file for the application is created with the JavaFX Packager tool, which embeds the JavaFX Launcher in the JAR file. However, it is useful to include the main() method so you can run JAR files that were created without the JavaFX Launcher, such as when using an IDE in which the JavaFX tools are not fully integrated. Also, Swing applications that embed JavaFX code require the main() method.

So one solution is to make sure it's being built in a way that fully supports the JavaFX tools. The other solution is to add a main method to starts the application. That would avoid any potential problems like this, and doesn't cause any problems in the case where it's not needed.

Your main method should look like this:

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

That will simply pass control on to JavaFX to handle like it would normally.

来源：https://stackoverflow.com/questions/36249986/javafx-fxml-program-errorno-main-method