Java dialog error message

Java Swing dialogs

Dialog windows or dialogs are an indispensable part of most modern GUI applications. A dialog is defined as a conversation between two or more persons. In a computer application a dialog is a window which is used to «talk» to the application. A dialog is used to input data, modify data, change the application settings etc. Dialogs are important means of communication between a user and a computer program.

In Java Swing, we can create two kinds of dialogs: standard dialogs and custom dialogs. Custom dialogs are created by programmers. They are based on the JDialog class. Standard dialogs are predefined dialogs available in the Swing toolkit, for example the JColorChooser or the JFileChooser . These are dialogs for common programming tasks like showing text, receiving input, loading and saving files. They save programmer’s time and enhance using some standard behaviour.

There are two basic types of dialogs: modal and modeless. Modal dialogs block input to other top-level windows. Modeless dialogs allow input to other windows. An open file dialog is a good example of a modal dialog. While choosing a file to open, no other operation should be permitted. A typical modeless dialog is a find text dialog. It is handy to have the ability to move the cursor in the text control and define, where to start the finding of the particular text.

Java Swing message dialogs

Message dialogs are simple dialogs that provide information to the user. Message dialogs are created with the JOptionPane.showMessageDialog() method.

package com.zetcode; import javax.swing.GroupLayout; import javax.swing.JButton; import javax.swing.JComponent; import javax.swing.JFrame; import javax.swing.JOptionPane; import javax.swing.JPanel; import java.awt.EventQueue; import static javax.swing.GroupLayout.DEFAULT_SIZE; public class MessageDialogsEx extends JFrame < private JPanel pnl; public MessageDialogsEx() < initUI(); >private void initUI() < pnl = (JPanel) getContentPane(); var warBtn = new JButton("Warning"); var errBtn = new JButton("Error"); var queBtn = new JButton("Question"); var infBtn = new JButton("Information"); warBtn.addActionListener(event ->JOptionPane.showMessageDialog(pnl, "A deprecated call!", "Warning", JOptionPane.WARNING_MESSAGE)); errBtn.addActionListener(event -> JOptionPane.showMessageDialog(pnl, "Could not open file!", "Error", JOptionPane.ERROR_MESSAGE)); queBtn.addActionListener(event -> JOptionPane.showMessageDialog(pnl, "Are you sure to quit?", "Question", JOptionPane.QUESTION_MESSAGE)); infBtn.addActionListener(event -> JOptionPane.showMessageDialog(pnl, "Download completed.", "Information", JOptionPane.INFORMATION_MESSAGE)); createLayout(warBtn, errBtn, queBtn, infBtn); setTitle("Message dialogs"); setSize(300, 200); setLocationRelativeTo(null); setDefaultCloseOperation(EXIT_ON_CLOSE); > private void createLayout(JComponent. arg) < var pane = getContentPane(); var gl = new GroupLayout(pane); pane.setLayout(gl); gl.setAutoCreateGaps(true); gl.setHorizontalGroup(gl.createSequentialGroup() .addContainerGap(DEFAULT_SIZE, Short.MAX_VALUE) .addGroup(gl.createParallelGroup() .addComponent(arg[0]) .addComponent(arg[2])) .addGroup(gl.createParallelGroup() .addComponent(arg[1]) .addComponent(arg[3])) .addContainerGap(DEFAULT_SIZE, Short.MAX_VALUE) ); gl.setVerticalGroup(gl.createSequentialGroup() .addContainerGap(DEFAULT_SIZE, Short.MAX_VALUE) .addGroup(gl.createParallelGroup() .addComponent(arg[0]) .addComponent(arg[1])) .addGroup(gl.createParallelGroup() .addComponent(arg[2]) .addComponent(arg[3])) .addContainerGap(DEFAULT_SIZE, Short.MAX_VALUE) ); gl.linkSize(arg[0], arg[1], arg[2], arg[3]); pack(); >public static void main(String[] args) < EventQueue.invokeLater(() ->< var md = new MessageDialogsEx(); md.setVisible(true); >); > >

The example shows an error, a warning, a question, and an information message dialog.

var warBtn = new JButton("Warning"); var errBtn = new JButton("Error"); var queBtn = new JButton("Question"); var infBtn = new JButton("Information");

These four buttons show four different message dialogs.

errBtn.addActionListener(event -> JOptionPane.showMessageDialog(pnl, "Could not open file!", "Error", JOptionPane.ERROR_MESSAGE));

The displayed icon depends on this constant. Figure: Question message dialog

Java Swing custom dialog

In the following example we create a simple custom dialog. It is a sample about dialog found in many GUI applications, usually located in the Help menu.

package com.zetcode; import javax.swing.Box; import javax.swing.GroupLayout; import javax.swing.ImageIcon; import javax.swing.JButton; import javax.swing.JComponent; import javax.swing.JDialog; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JMenu; import javax.swing.JMenuBar; import javax.swing.JMenuItem; import java.awt.EventQueue; import java.awt.Font; import java.awt.Frame; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.event.KeyEvent; import static javax.swing.GroupLayout.Alignment.CENTER; class AboutDialog extends JDialog < public AboutDialog(Frame parent) < super(parent); initUI(); >private void initUI() < var icon = new ImageIcon("src/resources/notes.png"); var imgLabel = new JLabel(icon); var textLabel = new JLabel("Notes, 1.23"); textLabel.setFont(new Font("Serif", Font.BOLD, 13)); var okBtn = new JButton("OK"); okBtn.addActionListener(event ->dispose()); createLayout(textLabel, imgLabel, okBtn); setModalityType(ModalityType.APPLICATION_MODAL); setTitle("About Notes"); setDefaultCloseOperation(DISPOSE_ON_CLOSE); setLocationRelativeTo(getParent()); > private void createLayout(JComponent. arg) < var pane = getContentPane(); var gl = new GroupLayout(pane); pane.setLayout(gl); gl.setAutoCreateContainerGaps(true); gl.setAutoCreateGaps(true); gl.setHorizontalGroup(gl.createParallelGroup(CENTER) .addComponent(arg[0]) .addComponent(arg[1]) .addComponent(arg[2]) .addGap(200) ); gl.setVerticalGroup(gl.createSequentialGroup() .addGap(30) .addComponent(arg[0]) .addGap(20) .addComponent(arg[1]) .addGap(20) .addComponent(arg[2]) .addGap(30) ); pack(); >> public class CustomDialogEx extends JFrame implements ActionListener < public CustomDialogEx() < initUI(); >private void initUI() < createMenuBar(); setTitle("Simple Dialog"); setSize(350, 250); setLocationRelativeTo(null); setDefaultCloseOperation(EXIT_ON_CLOSE); >private void createMenuBar() < var menubar = new JMenuBar(); var fileMenu = new JMenu("File"); fileMenu.setMnemonic(KeyEvent.VK_F); var helpMenu = new JMenu("Help"); helpMenu.setMnemonic(KeyEvent.VK_H); var aboutMemuItem = new JMenuItem("About"); aboutMemuItem.setMnemonic(KeyEvent.VK_A); helpMenu.add(aboutMemuItem); aboutMemuItem.addActionListener(this); menubar.add(fileMenu); menubar.add(Box.createGlue()); menubar.add(helpMenu); setJMenuBar(menubar); >@Override public void actionPerformed(ActionEvent e) < showAboutDialog(); >private void showAboutDialog() < var aboutDialog = new AboutDialog(this); aboutDialog.setVisible(true); >public static void main(String[] args) < EventQueue.invokeLater(() ->< var ex = new CustomDialogEx(); ex.setVisible(true); >); > >

From the Help menu, we can popup a small dialog box. The dialog displays text, an icon, and a button.

class AboutDialog extends JDialog 
The custom dialog is based on the JDialog class.
setModalityType(ModalityType.APPLICATION_MODAL);
 
The setModalityType() method sets the modality type of the dialog. The ModalityType.APPLICATION_MODAL blocks input from all top-level windows of the same application. In our case, the input to the application's frame is blocked during the lifetime of the dialog.
 
setLocationRelativeTo(getParent());
 
The setLocationRelativeTo() method centers the dialog window over the area of the frame window.
 
setDefaultCloseOperation(DISPOSE_ON_CLOSE);
 
The setDefaultCloseOperation() sets what happens when the user clicks on the window's Close button. The dialog will be hidden and disposed.
 
private void showAboutDialog()
 
 
The dialog window is shown on the screen with the setVisible() method. Figure: Custom dialog
 
JFileChooser
 
JFileChooser is a standard dialog for selecting a file from the file system.
 
package com.zetcode; import javax.swing.AbstractAction; import javax.swing.GroupLayout; import javax.swing.ImageIcon; import javax.swing.JButton; import javax.swing.JComponent; import javax.swing.JFileChooser; import javax.swing.JFrame; import javax.swing.JOptionPane; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.JTextArea; import javax.swing.JToolBar; import javax.swing.filechooser.FileNameExtensionFilter; import java.awt.EventQueue; import java.awt.event.ActionEvent; import java.io.File; import java.io.IOException; import java.nio.file.Files; import java.nio.file.Paths; import static javax.swing.GroupLayout.DEFAULT_SIZE; public class FileChooserEx extends JFrame < private JPanel panel; private JTextArea area; public FileChooserEx() < initUI(); >private void initUI() < panel = (JPanel) getContentPane(); area = new JTextArea(); var spane = new JScrollPane(); spane.getViewport().add(area); var toolbar = createToolBar(); createLayout(toolbar, spane); setTitle("JFileChooser"); setSize(400, 300); setLocationRelativeTo(null); setDefaultCloseOperation(EXIT_ON_CLOSE); >private JToolBar createToolBar() < var openIcon = new ImageIcon("src/resources/document-open.png"); var toolbar = new JToolBar(); var openBtn = new JButton(openIcon); openBtn.addActionListener(new OpenFileAction()); toolbar.add(openBtn); return toolbar; >private void createLayout(JComponent. arg) < var pane = getContentPane(); var gl = new GroupLayout(pane); pane.setLayout(gl); gl.setHorizontalGroup(gl.createParallelGroup() .addComponent(arg[0], DEFAULT_SIZE, DEFAULT_SIZE, Short.MAX_VALUE) .addGroup(gl.createSequentialGroup() .addComponent(arg[1])) ); gl.setVerticalGroup(gl.createSequentialGroup() .addComponent(arg[0]) .addGap(4) .addComponent(arg[1]) ); pack(); >public String readFile(File file) < String content = ""; try < content = new String(Files.readAllBytes(Paths.get( file.getAbsolutePath()))); >catch (IOException ex) < JOptionPane.showMessageDialog(this, "Could not read file", "Error", JOptionPane.ERROR_MESSAGE); >return content; > private class OpenFileAction extends AbstractAction < @Override public void actionPerformed(ActionEvent e) < var fileChooser = new JFileChooser(); var filter = new FileNameExtensionFilter("Java files", "java"); fileChooser.addChoosableFileFilter(filter); int ret = fileChooser.showDialog(panel, "Open file"); if (ret == JFileChooser.APPROVE_OPTION) < var file = fileChooser.getSelectedFile(); var text = readFile(file); area.setText(text); >> > public static void main(String[] args) < EventQueue.invokeLater(() ->< var ex = new FileChooserEx(); ex.setVisible(true); >); > >
 
The code example will demonstrate how to use a JFileChooser to load file contents into the text area component.
 
var fileChooser = new JFileChooser();
 
This is the constructor of the file chooser dialog.
 
var filter = new FileNameExtensionFilter("Java files", "java"); fileChooser.addChoosableFileFilter(filter);
 
Here we define the file filter. In our case, we will have Java files with extension .java . We have also the default All files option.
 
int ret = fileChooser.showDialog(panel, "Open file");
 
The showDialog() method displays the dialog on the screen. The JFileChooser.APPROVE_OPTION is returned when the Yes or OK buttons are clicked.
 
if (ret == JFileChooser.APPROVE_OPTION)
 
Here we get the name of the selected file. We read the contents of the file and set the text into the text area.
 
 
 Figure: JFileChooser dialog
 
JColorChooser
 
JColorChooser is a standard dialog for selecting a colour.
 
package com.zetcode; import javax.swing.GroupLayout; import javax.swing.ImageIcon; import javax.swing.JButton; import javax.swing.JColorChooser; import javax.swing.JComponent; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.JToolBar; import java.awt.Color; import java.awt.EventQueue; import static javax.swing.GroupLayout.DEFAULT_SIZE; public class ColorChooserEx extends JFrame < private JPanel colourPanel; public ColorChooserEx() < initUI(); >private void initUI() < colourPanel = new JPanel(); colourPanel.setBackground(Color.WHITE); var toolbar = createToolBar(); createLayout(toolbar, colourPanel); setTitle("JColorChooser"); setSize(400, 300); setLocationRelativeTo(null); setDefaultCloseOperation(EXIT_ON_CLOSE); >private JToolBar createToolBar() < var openIcon = new ImageIcon("src/resources/colourdlg.png"); var toolbar = new JToolBar(); var openBtn = new JButton(openIcon); openBtn.addActionListener(e ->< var color = JColorChooser.showDialog(colourPanel, "Choose colour", Color.white); colourPanel.setBackground(color); >); toolbar.add(openBtn); return toolbar; > private void createLayout(JComponent. arg) < var pane = getContentPane(); var gl = new GroupLayout(pane); pane.setLayout(gl); gl.setHorizontalGroup(gl.createParallelGroup() .addComponent(arg[0], DEFAULT_SIZE, DEFAULT_SIZE, Short.MAX_VALUE) .addGroup(gl.createSequentialGroup() .addGap(30) .addComponent(arg[1]) .addGap(30)) ); gl.setVerticalGroup(gl.createSequentialGroup() .addComponent(arg[0]) .addGap(30) .addComponent(arg[1]) .addGap(30) ); pack(); >public static void main(String[] args) < EventQueue.invokeLater(() ->< var ex = new ColorChooserEx(); ex.setVisible(true); >); > >
 
In the example, we have a white panel. We will change the background colour of the panel by selecting a colour from the JColorChooser .
 
var color = JColorChooser.showDialog(colourPanel, "Choose colour", Color.white); colourPanel.setBackground(color);
 
This code shows the colour chooser dialog. The showDialog() method returns the selected colour value. We change the colourPanel's background to the newly selected colour.
 
In this part of the Java Swing tutorial, we have covered dialogs.
 
Источник
 
Class JOptionPane
 
JOptionPane makes it easy to pop up a standard dialog box that prompts users for a value or informs them of something. For information about using JOptionPane , see How to Make Dialogs, a section in The Java Tutorial.
 
While the JOptionPane class may appear complex because of the large number of methods, almost all uses of this class are one-line calls to one of the static showXxxDialog methods shown below: 
 Common JOptionPane method names and their descriptions 
 
Method Name
 
Description
 
  
 
 
showConfirmDialog
 
Asks a confirming question, like yes/no/cancel.
 
 
 
showInputDialog
 
Prompt for some input.
 
 
 
showMessageDialog
 
Tell the user about something that has happened.
 
 
 
showOptionDialog
 
The Grand Unification of the above three.
 
 
 
 
 Each of these methods also comes in a showInternalXXX flavor, which uses an internal frame to hold the dialog box (see JInternalFrame ). Multiple convenience methods have also been defined -- overloaded versions of the basic methods that use different parameter lists.
 
All dialogs are modal. Each showXxxDialog method blocks the caller until the user's interaction is complete. 
 Common dialog 
 
icon
 
message
 
 
 
input value
 
 
 
option buttons
 
 
 
 The basic appearance of one of these dialog boxes is generally similar to the picture above, although the various look-and-feels are ultimately responsible for the final result. In particular, the look-and-feels will adjust the layout to accommodate the option pane's ComponentOrientation property. 
 
Parameters: 
The parameters to these methods follow consistent patterns:
 
 
ERROR_MESSAGE
 
INFORMATION_MESSAGE
 
WARNING_MESSAGE
 
QUESTION_MESSAGE
 
PLAIN_MESSAGE
 
 
 
DEFAULT_OPTION
 
YES_NO_OPTION
 
YES_NO_CANCEL_OPTION
 
OK_CANCEL_OPTION
 
 
When the selection is changed, setValue is invoked, which generates a PropertyChangeEvent .
 
If a JOptionPane has configured to all input setWantsInput the bound property JOptionPane.INPUT_VALUE_PROPERTY can also be listened to, to determine when the user has input or selected a value.
 
 
YES_OPTION
 
NO_OPTION
 
CANCEL_OPTION
 
OK_OPTION
 
CLOSED_OPTION
 
 
JOptionPane.showInternalMessageDialog(frame, "information", "information", JOptionPane.INFORMATION_MESSAGE);
 
JOptionPane.showConfirmDialog(null, "choose one", "choose one", JOptionPane.YES_NO_OPTION);
 
Show an internal information dialog with the options yes/no/cancel and message 'please choose one' and title information:
 
JOptionPane.showInternalConfirmDialog(frame, "please choose one", "information", JOptionPane.YES_NO_CANCEL_OPTION, JOptionPane.INFORMATION_MESSAGE);
 
Show a warning dialog with the options OK, CANCEL, title 'Warning', and message 'Click OK to continue':
 
Object[] options = < "OK", "CANCEL" >; JOptionPane.showOptionDialog(null, "Click OK to continue", "Warning", JOptionPane.DEFAULT_OPTION, JOptionPane.WARNING_MESSAGE, null, options, options[0]);
 
Show a dialog asking the user to type in a String: String inputValue = JOptionPane.showInputDialog("Please input a value"); Show a dialog asking the user to select a String:
 
Object[] possibleValues = < "First", "Second", "Third" >; 
Object selectedValue = JOptionPane.showInputDialog(null, "Choose one", "Input", JOptionPane.INFORMATION_MESSAGE, null, possibleValues, possibleValues[0]);
 
Direct Use: 
To create and use an JOptionPane directly, the standard pattern is roughly as follows:
 
JOptionPane pane = new JOptionPane(arguments); pane.set.Xxxx(. ); // Configure JDialog dialog = pane.createDialog(parentComponent, title); dialog.show(); Object selectedValue = pane.getValue(); if(selectedValue == null) return CLOSED_OPTION; //If there is not an array of option buttons: if(options == null) < if(selectedValue instanceof Integer) return ((Integer)selectedValue).intValue(); return CLOSED_OPTION; >//If there is an array of option buttons: for(int counter = 0, maxCounter = options.length; counter < maxCounter; counter++) < if(options[counter].equals(selectedValue)) return counter; >return CLOSED_OPTION;
 
Warning: Swing is not thread safe. For more information see Swing's Threading Policy.
 
Warning: Serialized objects of this class will not be compatible with future Swing releases. The current serialization support is appropriate for short term storage or RMI between applications running the same version of Swing. As of 1.4, support for long term storage of all JavaBeans has been added to the java.beans package. Please see XMLEncoder .
 
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