Javafx alert error - Исправление ошибок и поиск оптимальных решений проблем

Introduction to JavaFX Alert

In JavaFX, an Alert box is used to alert the user about further process. JavaFX Alert class is a subclass of Dialog class. Alert box in javafx alert the user about information, error messages, confirmation messages and warning messages to let know them the user about what exact dialog popup is about.

There are different ways to alert the user about what happening next. In that, there are 5 Alert types to alert the user.

Types of Alert Box in JavaFX

Below are the points which explain the types of alert box in javaFX:

None Alert: The None alert types do not set to any default properties.
Information Alert: The Information alert type informs the user about content information or suggests the user about what is going on in the next process.
Error Alert: The Error alert type is showing the user about where things went wrong or what is the error with the functionality.
Confirmation Alert: The Confirmation alert type is asking the user about permission to move further. We have two options available, Yes or If we click Yes means we have granted them permission to move next step of If we click No, then do not move to the next step.
Warning Alert: The Warning alert type warns the user about some fact or action. The warning does not disturb the further process as like Error.

Methods and Constructors in Alert Box

Below we can see the methods and constructor of alert box:

Methods

getAlertType(): Gives alert type.
setAlertType(Alert.AlertType): Setting the alert type.
getButtonTypes(): Get button type from the Observable list.
setContentText(String s): Setting the content or text to alert the user about what is the dialog box.
getContentText(): Gives the content text which we have set.

Constructors

Alert(Alert.AlertType alertType): Create a new Alert object with an alert type parameter.
Alert(Alert.AlertType alertType, String string, ButtonType… buttonType): Create new Alert object with alert type, String and Button type parameters.

How does Alert Box work in JavaFX?

Alert box in JavaFX mainly works on the value of alert type which is provided by Alert(AlertType.VALUE) constructor. Accessing JavaFX features user-defined class must extend Application

1.NONE Alert

Alert alertType=new Alert(AlertType.NONE);

2. INFORMATION Alert

Alert alertType=new Alert(AlertType.INFORMATION);

3. ERROR Alert

Alert alertType=new Alert(AlertType.ERROR);

4. CONFIRMATION Alert

Alert alertType=new Alert(AlertType.INFORMATION);

5. WARNING Alert

Alert alertType=new Alert(AlertType.WARNING);

How to Create Alert Box in Java FX?

Steps to Create Alert Boxes:

Step 1: Create an Alert type

Alert alertType=new Alert(AlertType.TYPE);

Step 2: Create a Pane or any other component.

TilePane tilePane=new TilePane ();

Step 3: Creating a scene means screen to display output.

Scene screen = new Scene(tilePane, length, width);

Step 4: Adding Scene reference screen to the Stage:

stage.setScene(screen);

Step 5: showing stage reference with the show () method.

stage.show();

Note: 2,3,4 and 5 steps are optional if we want any action classes with alert boxes then use 2,3,4 and 5 steps.

Examples of JavaFX Alert

Below are the examples of JavaFX Alert:

1. Information Alert

Code:

import javafx.application.Application;
import javafx.scene.control.Alert;
import javafx.scene.control.Alert.AlertType;
import javafx.stage.Stage;
public class InformtionAlertType extends Application {
@Override
public void start(Stage outputStage) throws Exception {
Alert alert = new Alert(AlertType.INFORMATION);// line 1
alert.setTitle("Information Dialog Box");// line 2
alert.setHeaderText("This is header section to write heading");// line 3
alert.setContentText("This is body section to write some info!");// line 4
alert.showAndWait(); // line 5
}
public static void main(String args[]) {
launch(args); // line 0
}
}

Output:

Explanation to the above program: In the above code line 0 calls start method from internal JVM. Line 1 creates an information alert type. Line 2 sets the title to a dialog box. Line 3 sets the header text. Line 4 sets the body text of the dialog box. Line 5 shows the dialog box output. As you can see in the output information dialog box has a predefined image on the right end.

2. Error Alert

Code:

import javafx.application.Application;
import javafx.scene.control.Alert;
import javafx.scene.control.Alert.AlertType;
import javafx.stage.Stage;
public class ErrorAlertType extends Application {
@Override
public void start(Stage outputStage) throws Exception {
Alert alert = new Alert(AlertType.ERROR);// line 1
alert.setTitle("Error Dialog Box");// line 2
alert.setHeaderText("ERROR HEADING");// line 3
alert.setContentText("I am proving what is the error exactly!");// line 4
alert.showAndWait(); // line 5
}
public static void main(String args[]) {
launch(args); // line 0
}
}

Output:

Explanation to the above program: In the above code line 0 calls start method from internal JVM. Line 1 creates an error alert type. Line 2 sets the title to the dialog box. Line 3 sets the header text. Line 4 sets the body text of the dialog box. Line 5 shows the dialog box output. As you can see in the output information dialog box has a predefined image on the right end.

3. Confirmation Alert

Code:

import javafx.application.Application;
import javafx.scene.control.Alert;
import javafx.scene.control.Alert.AlertType;
import javafx.stage.Stage;
public class ConfirmationAlertType extends Application {
@Override
public void start(Stage outputStage) throws Exception {
Alert alert = new Alert(AlertType.CONFIRMATION);// line 1
alert.setTitle("Confirmation Dialog Box");// line 2
alert.setHeaderText("Please Confirm!");// line 3
alert.setContentText("Are you sure want to move further?!");// line 4
alert.showAndWait(); // line 5
}
public static void main(String args[]) {
launch(args); // line 0
}
}

Output:

Explanation to the above program: In the above code line 0 calls start method from internal JVM. Line 1 creates a confirmation alert type. Line 2 sets the title to the dialog box. Line 3 sets the header text. Line 4 sets the body text of the dialog box. Line 5 shows the dialog box output. As you can see in the output information dialog box has a predefined image on the right end.

4. Warning Alert

Code:

import javafx.application.Application;
import javafx.scene.control.Alert;
import javafx.scene.control.Alert.AlertType;
import javafx.stage.Stage;
public class WarningAlertType extends Application {
@Override
public void start(Stage outputStage) throws Exception {
Alert alert = new Alert(AlertType.WARNING);// line 1
alert.setTitle("Warning Dialog Box");// line 2
alert.setHeaderText("Warning!");// line 3
alert.setContentText("Some packages may be installed additionally!");// line 4
alert.showAndWait(); // line 5
}
public static void main(String args[]) {
launch(args); // line 0
}
}

Output:

Explanation to the above program: In the above code line 0 calls start method from internal JVM. Line 1 creates a warning alert type. Line 2 sets the title to the dialog box. Line 3 sets the header text. Line 4 sets the body text of the dialog box. Line 5 shows the dialog box output. As you can see in the output information dialog box has a predefined image on the right end.

Create JavaFX Message Box

To accomplish the following example code, we use Java version 18, JavaFX version 13 and Netbeans IDE version 13.

Example Code:

//write your package name
package com.mycompany.javafx_messagebox;

//import required libraries
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.Alert;
import javafx.scene.control.Alert.AlertType;
import javafx.scene.control.Button;
import javafx.scene.layout.TilePane;
import javafx.stage.Stage;

/**
 * JavaFX App
 */
public class App extends Application {

    @Override
    public void start(Stage stage) {

        // create a tile pane
        TilePane r = new TilePane();
        //add padding
        r.setPadding(new Insets(10, 10, 10, 10));

        // an array of button names
        String[] buttonNames = {"Confirmation MessageBox",
                                "Error MessageBox",
                                "Information MessageBox",
                                "Warning MessageBox"};

        //Show no alert at the startup of the program
        Alert alert = new Alert(AlertType.NONE);


        /*
        a loop to create buttons, define actions when
        they are pressed and add them to the tile pane
        */
        for (String s : buttonNames) {
            Button button = new Button(s);

            button.setOnAction((ActionEvent event) -> {
                if (null != button.getText()) {
                    switch (button.getText()) {
                        case "Confirmation MessageBox":
                            // set alert type, title, content text and then show it
                            alert.setAlertType(AlertType.CONFIRMATION);
                            alert.setTitle("Confirmation MessageBox");
                            alert.setContentText("This is a CONFIRMATION "+
                                                 "message for you!");
                            alert.show();
                            break;
                        case "Error MessageBox":
                            // set alert type, title, content text and then show it
                            alert.setAlertType(AlertType.ERROR);
                            alert.setTitle("Error MessageBox");
                            alert.setContentText("This is an ERROR message for you!");
                            alert.show();
                            break;
                        case "Information MessageBox":
                            // set alert type, title, content text and then show it
                            alert.setAlertType(AlertType.INFORMATION);
                            alert.setTitle("Information MessageBox");
                            alert.setContentText("This is a INFORMATION "+
                                                 "message for you!");
                            alert.show();
                            break;
                        case "Warning MessageBox":
                            // set alert type, title, content text and then show it
                            alert.setAlertType(AlertType.WARNING);
                            alert.setTitle("Warning MessageBox");
                            alert.setContentText("This is a WARNING message for you!");
                            alert.show();
                            break;
                        default:
                            break;
                    }
                }
            });

            //add button
            r.getChildren().add(button);

        }

        // create a scene
        Scene sc = new Scene(r, 640, 50);

        // set the scene
        stage.setScene(sc);

        //show the stage
        stage.show();

    }//end start method

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

}//end App class

Output (main window):

Output (confirmation message box, displayed when we click on Confirmation MessageBox button):

Output (error message box, displayed when we click on Error MessageBox button):

Output (information message box, displayed when we click on Information MessageBox button):

OUTPUT (warning message box, displayed when we click on the Warning MessageBox button):

For this tutorial, we don’t need to make any changes to the module-info.java and pom.xml files. Create a JavaFX project and practice the code given above.

We have a main class named App that extends the Application class (which is standard in Java). You can name the primary launch class (App).

Next, we override the start() method because the App is the child class of the Application class. Remember that the child class needs to implement all abstract functions/methods of the parent class.

After that, we have a start() method that takes one parameter of the Stage type. We are using the Stage type parameter because this is where all visual components JavaFX application will be displayed.

We do not need to create the Stage type object because the JavaFX runtime creates it. The following is the step-by-step explanation of what’s inside the start() method.

Create an object of JavaFX TilePane, which is a layout component and lays out all its child components in the grid of same-sized cells.
Add margins around the whole grid (top/right/bottom/left).
Create an array with the names of all buttons we need for this application.
Create an alert message box of type NONE because we do not want to display any message box at the program’s startup.
Next, we have a for loop, which iterates over all the button names.
- Inside the loop, we create a button of the current name.
- Set an action for that specific button based on the condition. We get the button text and display a message box based on the button name using the switch statement.
Add the button to the TilePane.
Create a scene using the Scene class.
Set the scene.
Finally, show the stage.

Now, it is the main method’s turn. We can launch the JavaFX application without having the main method, but it is useful when we are required to use parameters that are passed to the application using the command line.

Источник

java.lang.Object
- java.lang.Enum<Alert.AlertType>
- - javafx.scene.control.Alert.AlertType

All Implemented Interfaces:

Serializable, Comparable<Alert.AlertType>

Enclosing class:

Alert
```
public static enum Alert.AlertType
extends Enum<Alert.AlertType>
```
An enumeration containing the available, pre-built alert types that
the Alert class can use to pre-populate various properties.

Since:

JavaFX 8u40

Enum Constant Summary

Enum Constants

Enum Constant	Description
`CONFIRMATION`	The CONFIRMATION alert type configures the Alert dialog to appear in a way that suggests the content of the dialog is seeking confirmation from the user.
`ERROR`	The ERROR alert type configures the Alert dialog to appear in a way that suggests that something has gone wrong.
`INFORMATION`	The INFORMATION alert type configures the Alert dialog to appear in a way that suggests the content of the dialog is informing the user of a piece of information.
`NONE`	The NONE alert type has the effect of not setting any default properties in the Alert.
`WARNING`	The WARNING alert type configures the Alert dialog to appear in a way that suggests the content of the dialog is warning the user about some fact or action.

Method Summary

All Methods Static Methods Concrete Methods

Modifier and Type	Method	Description
`static Alert.AlertType`	`valueOf(String name)`	Returns the enum constant of this type with the specified name.
`static Alert.AlertType[]`	`values()`	Returns an array containing the constants of this enum type, in the order they are declared.

Methods inherited from class java.lang.Enum

clone, compareTo, equals, finalize, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

- Enum Constant Detail
  - NONE
```
public static final Alert.AlertType NONE
```
    The NONE alert type has the effect of not setting any default properties
    in the Alert.
  - INFORMATION
```
public static final Alert.AlertType INFORMATION
```
    The INFORMATION alert type configures the Alert dialog to appear in a
    way that suggests the content of the dialog is informing the user of
    a piece of information. This includes an ‘information’ image, an
    appropriate title and header, and just an OK button for the user to
    click on to dismiss the dialog.
  - WARNING
```
public static final Alert.AlertType WARNING
```
    The WARNING alert type configures the Alert dialog to appear in a
    way that suggests the content of the dialog is warning the user about
    some fact or action. This includes a ‘warning’ image, an
    appropriate title and header, and just an OK button for the user to
    click on to dismiss the dialog.
  - CONFIRMATION
```
public static final Alert.AlertType CONFIRMATION
```
    The CONFIRMATION alert type configures the Alert dialog to appear in a
    way that suggests the content of the dialog is seeking confirmation from
    the user. This includes a ‘confirmation’ image, an
    appropriate title and header, and both OK and Cancel buttons for the
    user to click on to dismiss the dialog.
  - ERROR
```
public static final Alert.AlertType ERROR
```
    The ERROR alert type configures the Alert dialog to appear in a
    way that suggests that something has gone wrong. This includes an
    ‘error’ image, an appropriate title and header, and just an OK button
    for the user to click on to dismiss the dialog.
- Method Detail
  - values
```
public static Alert.AlertType[] values()
```
    Returns an array containing the constants of this enum type, in
    the order they are declared. This method may be used to iterate
    over the constants as follows:
    
    for (Alert.AlertType c : Alert.AlertType.values()) System.out.println(c);
    Returns:
    
    an array containing the constants of this enum type, in the order they are declared
  - valueOf
```
public static Alert.AlertType valueOf(String name)
```
    Returns the enum constant of this type with the specified name.
    The string must match exactly an identifier used to declare an
    enum constant in this type. (Extraneous whitespace characters are
    not permitted.)
    
    Parameters:
    
    name — the name of the enum constant to be returned.
    
    Returns:
    
    the enum constant with the specified name
    
    Throws:
    
    IllegalArgumentException — if this enum type has no constant with the specified name
    
    NullPointerException — if the argument is null

Источник

import javafx.application.Application;

import javafx.scene.Scene;

import javafx.scene.control.Button;

import javafx.scene.layout.*;

import javafx.event.ActionEvent;

import javafx.event.EventHandler;

import javafx.scene.control.*;

import javafx.stage.Stage;

import javafx.scene.control.Alert.AlertType;

public class Alert_2 extends Application {

public void start(Stage s)

{

s.setTitle("creating alerts");

Button b = new Button("Confirmation alert");

Button b1 = new Button("error alert");

Button b2 = new Button("Information alert");

Button b3 = new Button("Warning alert");

Button b4 = new Button("none alert");

TilePane r = new TilePane();

Alert a = new Alert(AlertType.NONE);

EventHandler<ActionEvent> event = new

EventHandler<ActionEvent>() {

public void handle(ActionEvent e)

{

a.setAlertType(AlertType.CONFIRMATION);

a.setContentText("ConfirmationDialog");

a.show();

}

};

EventHandler<ActionEvent> event1 = new

EventHandler<ActionEvent>() {

public void handle(ActionEvent e)

{

a.setAlertType(AlertType.ERROR);

a.setContentText("error Dialog");

a.show();

}

};

EventHandler<ActionEvent> event2 = new

EventHandler<ActionEvent>() {

public void handle(ActionEvent e)

{

a.setAlertType(AlertType.INFORMATION);

a.setContentText("Information Dialog");

a.show();

}

};

EventHandler<ActionEvent> event3 = new

EventHandler<ActionEvent>() {

public void handle(ActionEvent e)

{

a.setAlertType(AlertType.WARNING);

a.setContentText("Warning Dialog");

a.show();

}

};

EventHandler<ActionEvent> event4 = new

EventHandler<ActionEvent>() {

public void handle(ActionEvent e)

{

Alert a1 = new Alert(AlertType.NONE,

"default Dialog",ButtonType.APPLY);

a1.show();

}

};

b.setOnAction(event);

b1.setOnAction(event1);

b2.setOnAction(event2);

b3.setOnAction(event3);

b4.setOnAction(event4);

r.getChildren().add(b);

r.getChildren().add(b1);

r.getChildren().add(b2);

r.getChildren().add(b3);

r.getChildren().add(b4);

Scene sc = new Scene(r, 200, 200);

s.setScene(sc);

s.show();

}

public static void main(String args[])

{

launch(args);

}

Источник

JavaFX Alert Dialogs Tutorial

In this blog tutorial, you will learn to use the JavaFX alert dialogs. Alert is a subclass of the Dialog class. JavaFX alert dialog is used to show some information to the user.

Types of Alert dialogs in JavaFX

Confirmation – This type of alert is used to confirm from the user in a way that suggests the content of the dialog is seeking confirmation from the user. This includes confirmation of both the Ok and Cancel buttons.
Warning – This type of alert is used to show a warning alert to inform the user about some fact of action.
None – This is a type of alert that has the effect of not setting any default properties in the Alert.
Information – This type of alert is used to show a piece of information.
Error – This type of alert is used to show a piece of information that has gone wrong.

Source code to show alert dialog in JavaFX

Confirmation Alert

Alert alert = new Alert(Alert.AlertType.CONFIRMATION);
alert.setTitle("Confirmation alert Dialog");
alert.setContentText("Please confirm");
alert.setHeaderText("Confirmation");
alert.showAndWait();

Output

Warning Alert

Alert alert = new Alert(Alert.AlertType.WARNING);
alert.setTitle("Warning Dialog");
alert.setContentText("This is a warning alert!");
alert.setHeaderText("Warning alert");
alert.showAndWait();

Output

None Alert type

Alert alert = new Alert(Alert.AlertType.NONE);
alert.setTitle("None Alert type");
alert.setContentText("This is a none type alert!");
alert.setHeaderText(null);
alert.getDialogPane().getButtonTypes().add(ButtonType.CLOSE);
alert.showAndWait();

Output

Information Alert

Alert alert = new Alert(Alert.AlertType.INFORMATION);
alert.setTitle("Information Dialog");
alert.setContentText("This is an information alert!");
alert.setHeaderText("Information alert");
alert.showAndWait();

Output

Error Alert

Alert alert = new Alert(Alert.AlertType.ERROR);
alert.setTitle("Error Dialog");
alert.setContentText("This is an error alert!");
alert.setHeaderText("Error alert");
alert.showAndWait();

Output

YouTube Video

JavaFX Tutorial: Java Alert Box

Источник

Introduction to JavaFX Alert

Types of Alert Box in JavaFX

Methods and Constructors in Alert Box

Methods

Constructors

How does Alert Box work in JavaFX?

How to Create Alert Box in Java FX?

Examples of JavaFX Alert

1. Information Alert

2. Error Alert

3. Confirmation Alert

4. Warning Alert

Recommended Articles

Create JavaFX Message Box

Create an object of JavaFX TilePane, which is a layout component and lays out all its child components in the grid of same-sized cells.

Add margins around the whole grid (top/right/bottom/left).

Create an array with the names of all buttons we need for this application.

Create an alert message box of type NONE because we do not want to display any message box at the program’s startup.

Next, we have a for loop, which iterates over all the button names.

Add the button to the TilePane.

Create a scene using the Scene class.

Set the scene.

Finally, show the stage.

Enum Constant Summary

Method Summary

Methods inherited from class java.lang.Enum

Methods inherited from class java.lang.Object

Enum Constant Detail

NONE

INFORMATION

WARNING

CONFIRMATION

ERROR

Method Detail

values

valueOf

JavaFX Alert Dialogs Tutorial

Types of Alert dialogs in JavaFX

Source code to show alert dialog in JavaFX

Confirmation Alert

Output

Warning Alert

Output

None Alert type

Output

Information Alert

Output

Error Alert

Output

YouTube Video

Create an object of JavaFX `TilePane`, which is a layout component and lays out all its child components in the grid of same-sized cells.

Add margins around the whole grid (`top/right/bottom/left`).

Create an alert message box of type `NONE` because we do not want to display any message box at the program’s startup.

Next, we have a `for` loop, which iterates over all the button names.

Add the button to the `TilePane`.

Create a scene using the `Scene` class.