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Trail: Creating a GUI with JFC/Swing
Lesson: Using Swing Components

## How to Make Dialogs

> Several classes support dialogs -- windows that are more limited than frames. To create simple, standard dialogs, you use the `JOptionPane` class. The `ProgressMonitor` class can put up a dialog that shows the progress of an operation. Two other classes, `JColorChooser` and `JFileChooser`, also supply standard dialogs. To bring up a print dialog, you can use either the `getPrintJob` method defined in the `Toolkit` class or, if you're using the Java 2 platform, the Printing API. To create custom dialogs, use the `JDialog` class directly.

> The code for simple dialogs can be minimal. For example, here's an informational dialog:

> Here is the code that creates and shows it:

> >     JOptionPane.showMessageDialog(frame, "Eggs aren't supposed to be green.");

> The rest of this section covers the following topics:
> - An Overview of Dialogs
> - The DialogDemo Example
> - JOptionPane Features
> - Creating and Showing Simple Dialogs
> - Customizing Button Text
> - Getting the User's Input from a Dialog
> - Stopping Automatic Dialog Closing
> - The Dialog API
> - Examples that Use Dialogs

### An Overview of Dialogs

> Every dialog is dependent on a frame. When that frame is destroyed, so are its dependent dialogs. When the frame is iconified, its dependent dialogs disappear from the screen. When the frame is deiconified, its dependent dialogs return to the screen. The AWT automatically provides this behavior.

> A dialog can be modal. When a modal dialog is visible, it blocks user input to all other windows in the program. The dialogs that `JOptionPane` provides are modal. To create a non-modal dialog, you must use the `JDialog` class directly.

> The `JDialog` class is a subclass of the AWT `java.awt.Dialog` class. It adds to `Dialog` a root pane and support for a default close operation. These are the same features that `JFrame` has, and using `JDialog` directly is very similar to using `JFrame` directly. If you're going to use `JDialog` directly, then you should understand the material in Using Top-Level Containers and How to Make Frames, especially Responding to Window-Closing Events.

> Even when you use `JOptionPane` to implement a dialog, you're still using a `JDialog` behind the scenes. The reason is that `JOptionPane` is simply a container that can automatically create a `JDialog` and add itself to the `JDialog`'s content pane.

### The DialogDemo Example

> Here's a picture of an application that displays dialogs.

> > Try this:
> > 1. Compile and run the application. The main source file is `DialogDemo.java`. You will also need one other source file and an image file. See the examples index for links to all the files required by this example.
> >    See Getting Started with Swing if you need help compiling or running this application.
> > 2. Click the Show it! button.
> >    A modal dialog will appear. Until you close it, the application will be unresponsive, although it will repaint itself if necessary. You can close the dialog either by clicking a button in the dialog or explicitly, such as by using the dialog's window decorations.
> > 3. Iconify the DialogDemo window while a dialog is showing.
> >    The dialog will disappear from the screen until you deiconify the DialogDemo window.
> > 4. In the More Dialogs pane, click the bottom radio button and then the Show it! button. A non-modal dialog will appear. Note that the DialogDemo window remains fully functional while the non-modal dialog is up.

### JOptionPane Features

> Using `JOptionPane`, you can create and customize several different kinds of dialogs. `JOptionPane` provides support for laying out standard dialogs, providing icons, specifying the dialog's title and text, and customizing the button text. Other features allow you to customize the components the dialog displays and specify where the dialog should appear onscreen. You can even specify that an option pane put itself into an internal frame (`JInternalFrame`) instead of a `JDialog`.

> > Note: The internal frames that `JOptionPane` creates currently behave differently from modal dialogs. They don't behave modally, and in general seem more like frames than like dialogs. For this reason, we don't currently recommend their use.

> When you create a `JOptionPane`, look-and-feel-specific code adds components to the `JOptionPane` and determines the layout of those components.

> `JOptionPane`'s icon support lets you easily specify which icon the dialog displays. You can use a custom icon, no icon at all, or any one of four standard `JOptionPane` icons (question, information, warning, and error). Each look and feel has its own versions of the four standard icons. The following figure shows the icons used in the Java Look & Feel.

> > Icons provided by JOptionPane
> > (Java Look & Feel shown)
> > question | information | warning | error

### Creating and Showing Simple Dialogs

> For most simple modal dialogs, you create and show the dialog using one of `JOptionPane`'s `showXxxDialog` methods. If your dialog should be an internal frame, then add `Internal` after `show` -- for example, `showMessageDialog` changes to `showInternalMessageDialog`. If you need to control the dialog's window-closing behavior or if the dialog isn't modal, then you should directly instantiate `JOptionPane` and add it to a `JDialog` instance. Then invoke `setVisible(true)` on the `JDialog` to make it appear.

> The two most useful `showXxxDialog` methods are `showMessageDialog` and `showOptionDialog`. The `showMessageDialog` method displays a simple, one-button dialog. The `showOptionDialog` method displays a customized dialog -- it can display a variety of buttons with customized button text, and can contain a standard text message or a collection of components.

> The other two `showXxxDialog` methods are used less often. The `showConfirmDialog` method asks the user to confirm something, but has the disadvantage of having standard button text (Yes/No or the localized equivalent, for example), rather than button text customized to the user's situation (Start/Cancel, for example). A fourth method, `showInputDialog`, is designed to display a modal dialog that gets a string from the user, using either a text field or an uneditable combo box. However, input dialogs aren't very useful right now, since the text field doesn't let you perform validation before the dialog goes away, and combo boxes in dialogs don't yet work well.

> Here are some examples, taken from `DialogDemo.java`, of using `showMessageDialog`, `showOptionDialog`, and the `JOptionPane` constructor. For more example code, see `DialogDemo.java` and the other programs listed in Examples that Use Dialogs.

> `showMessageDialog`
>   Displays a modal dialog with one button, which is labeled "OK" (or the localized equivalent). You can easily specify the message, icon, and title that the dialog displays. Here are some examples of using `showMessageDialog`:

>       //default title and icon
>       JOptionPane.showMessageDialog(frame,
>           "Eggs aren't supposed to be green.");
>       //custom title, warning icon
>       JOptionPane.showMessageDialog(frame,
>           "Eggs aren't supposed to be green.",
>           "Inane warning",
>           JOptionPane.WARNING_MESSAGE);
>       //custom title, error icon
>       JOptionPane.showMessageDialog(frame,
>           "Eggs aren't supposed to be green.",
>           "Inane error",
>           JOptionPane.ERROR_MESSAGE);
>       //custom title, no icon
>       JOptionPane.showMessageDialog(frame,
>           "Eggs aren't supposed to be green.",
>           "A plain message",
>           JOptionPane.PLAIN_MESSAGE);
>       //custom title, custom icon
>       JOptionPane.showMessageDialog(frame,
>           "Eggs aren't supposed to be green.",
>           "Inane custom dialog",
>           JOptionPane.INFORMATION_MESSAGE,
>           icon);

> `showOptionDialog`
>   Displays a modal dialog with the specified buttons, icons, message, title, and so on. With this method, you can change the text that appears on the buttons of standard dialogs. You can also perform many other kinds of customization.

>       //Custom button text
>       Object[] options = {"Yes, please",
>                           "No, thanks",
>                           "No eggs, no ham!"};
>       int n = JOptionPane.showOptionDialog(frame,
>           "Would you like some green eggs to go "
>           + "with that ham?",
>           "A Silly Question",
>           JOptionPane.YES_NO_CANCEL_OPTION,
>           JOptionPane.QUESTION_MESSAGE,
>           null,
>           options,
>           options[2]);

> `JOptionPane` (constructor)
>   Creates a `JOptionPane` with the specified buttons, icons, message, title, and so on. You must then add the option pane to a `JDialog`, register a property-change listener on the option pane, and show the dialog. See Stopping Automatic Dialog Closing for details.

>       final JOptionPane optionPane = new JOptionPane(
>           "The only way to close this dialog is by\n"
>           + "pressing one of the following buttons.\n"
>           + "Do you understand?",
>           JOptionPane, QUESTION_MESSAGE,
>           JOptionPane.YES_NO_OPTION);

> The arguments to all of the `showXxxDialog` methods and `JOptionPane` constructors are standardized, though the number of arguments for each method and constructor varies. The following list describes each argument. To see the exact list of arguments for a particular method, see The Dialog API.
> `Component parentComponent`
>   The first argument to each `showXxxDialog` method is always the parent component, which must be a frame, a component inside a frame, or null. If you specify a frame, then the dialog will appear over the center of the frame, and depend on that frame. If you specify a component inside a frame, then the dialog will appear over the center of that component, and depend on that component's frame. If you specify null, then the look and feel picks an appropriate position for the dialog -- generally the center of the screen, and the dialog doesn't depend on any visible frame.

>   The `JOptionPane` constructors do not include this argument. Instead, you specify the parent frame when you create the `JDialog` that contains the `JOptionPane`, and you use the `JDialog` `setLocationRelativeTo` method to set the dialog's position.

> `Object message`
>   This required argument specifies what the dialog should display in its main area. Generally, you specify a string, which results the dialog displaying a label with the specified text. You can split the message over several lines by putting newline (`\n`) characters inside the message string. For example:

>   >     "Complete the sentence:\n \"Green eggs and...\""

> `String title`
>   The title of the dialog.
> `int optionType`
>   Specifies the set of buttons that appear at the bottom of the dialog. Choose from one of the following standard sets: `DEFAULT_OPTION`, `YES_NO_OPTION`, `YES_NO_CANCEL_OPTION`, `OK_CANCEL_OPTION`.
> `int messageType`
>   This argument determines the icon displayed in the dialog. Choose from one of the following values: `PLAIN_MESSAGE` (no icon), `ERROR_MESSAGE`, `INFORMATION_MESSAGE`, `WARNING_MESSAGE`, `QUESTION_MESSAGE`.
> `Icon icon`
>   The icon to display in the dialog.
> `Object[] options`
>   Further specifies the option buttons to appear at the buttom of the dialog. Generally, you specify an array of strings for the buttons. See Customizing Button Text in a Standard Dialog for more information.
> `Object initialValue`
>   Specifies the default value to be selected.

> You can either let the default icon be used or specify the icon using the message type or icon argument. By default, a dialog created with `showMessageDialog` displays the information icon, and a dialog created with `showConfirmDialog` or `showInputDialog` displays the question icon. An option pane created with a `JOptionPane` constructor displays no icon, by default. To specify that the dialog display a standard icon or no icon, specify the message type. To specify a custom icon, use the icon argument. The icon argument takes precedence over the message type; as long as the icon argument has a non-null value, the dialog displays the specified icon.

### Customizing Button Text

> When you use `JOptionPane` to create a dialog, you can choose either to use the standard button text (which might vary by look and feel) or to specify different text.

> The following code, taken from `DialogDemo.java`, creates two Yes/No dialogs. The first dialog is implemented with `showConfirmDialog`, which uses the look-and-feel wording for the two buttons. The second dialog uses `showOptionDialog` so it can customize the wording. With the exception of wording changes, the dialogs are identical.

>     //default icon, custom title
>     int n = JOptionPane.showConfirmDialog(
>         frame,
>         "Would you like green eggs and ham?",
>         "An Inane Question",
>         JOptionPane.YES_NO_OPTION);
>     Object[] options = {"Yes, please",
>                         "No way!"};
>     int n = JOptionPane.showOptionDialog(frame,
>         "Would you like green eggs and ham?",
>         "A Silly Question",
>         JOptionPane.YES_NO_OPTION,
>         JOptionPane.QUESTION_MESSAGE,
>         null,     //don't use a custom Icon
>         options,  //the titles of buttons
>         options[0]); //default button title

### Getting the User's Input from a Dialog

> As the previous code snippets showed, the `showMessageDialog`, `showConfirmDialog`, and `showOptionDialog` methods return an integer indicating the user's choice. The values for this integer are `YES_OPTION`, `NO_OPTION`, `CANCEL_OPTION`, `OK_OPTION`, and `CLOSED_OPTION`. Except for `CLOSED_OPTION`, each option corresponds to the button the user pressed. When `CLOSED_OPTION` is returned, it indicates that the user closed the dialog window explicitly, rather than by choosing a button inside the option pane.

> Even if you change the strings that the standard dialog buttons display, the return value is still one of the pre-defined integers. For example, a `YES_NO_OPTION` dialog always returns one of the following values: `YES_OPTION`, `NO_OPTION`, or `CLOSED_OPTION`.

> If you're designing a custom dialog, on the other hand, then you need to design your dialog's API so that you can query the dialog about what the user chose. For example, the dialog implemented in `CustomDialog.java` has a `getValidatedText` method that returns the text the user entered.

### Stopping Automatic Dialog Closing

> By default, when the user clicks a `JOptionPane`-created button, the dialog closes. But what if you want to check the user's answer before closing the dialog? In this case, you must implement your own property change listener so that when the user clicks a button, the dialog doesn't automatically close.

> `DialogDemo` contains two dialogs that implement a property change listener. One of these dialogs is a custom modal dialog, implemented in `CustomDialog`, that uses `JOptionPane` both to get the standard icon and to get layout assistance. The other dialog, whose code is below, uses a standard Yes/No `JOptionPane`, Though this dialog is rather useless as written, its code is simple enough that you can use it as a template for more complex dialogs.

> Besides setting the property change listener, the following code also calls the `JDialog`'s `setDefaultCloseOperation` method and implements a window listener that handles the window close attempt properly. If you don't care to be notified when the user closes the window explicitly, then ignore the bold code.

> >     final JOptionPane optionPane = new JOptionPane(
> >                     "The only way to close this dialog is by\n"
> >                     + "pressing one of the following buttons.\n"
> >                     + "Do you understand?",
> >                     JOptionPane.QUESTION_MESSAGE,
> >                     JOptionPane.YES_NO_OPTION);

> >     final JDialog dialog = new JDialog(frame,
> >                                  "Click a button",
> >                                  true);
> >     dialog.setContentPane(optionPane);
> >     dialog.setDefaultCloseOperation(
> >         JDialog.DO_NOTHING_ON_CLOSE);
> >     dialog.addWindowListener(new WindowAdapter() {
> >         public void windowClosing(WindowEvent we) {
> >             setLabel("Thwarted user attempt to close window.");
> >         }
> >     });
> >     optionPane.addPropertyChangeListener(
> >         new PropertyChangeListener() {
> >             public void propertyChange(PropertyChangeEvent e) {
> >                 String prop = e.getPropertyName();

> >                 if (dialog.isVisible()
> >                  && (e.getSource() == optionPane)
> >                  && (prop.equals(JOptionPane.VALUE_PROPERTY) ||
> >                      prop.equals(JOptionPane.INPUT_VALUE_PROPERTY)))
> >                 {
> >                     //If you were going to check something
> >                     //before closing the window, you'd do
> >                     //it here.
> >                     dialog.setVisible(false);
> >                 }
> >             }
> >         });
> >     dialog.pack();
> >     dialog.setVisible(true);

> >     int value = ((Integer)optionPane.getValue()).intValue();
> >     if (value == JOptionPane.YES_OPTION) {
> >         setLabel("Good.");
> >     } else if (value == JOptionPane.NO_OPTION) {
> >         setLabel("Try using the window decorations "
> >                  + "to close the non-auto-closing dialog. "
> >                  + "You can't!");
> >     }

### The Dialog API

> The following tables list the commonly used `JOptionPane` and `JDialog` constructors and methods. Other methods you're likely to call are defined by the `Dialog`, `Window` and `Component` classes and include `pack`, `setSize`, and `setVisible`.

> The API is listed as follows:

> - Showing Standard Modal Dialogs (using `JOptionPane` Class Methods
> - Methods for Using `JOptionPane`s Directly
> - Frequently Used `JDialog` Constructors and Methods

> Showing Standard Modal Dialogs (Using `JOptionPane` Class Methods)
> Method | Purpose
> --- | ---
> `int showMessageDialog(Component, Object) int showMessageDialog(Component, Object, String, int) int showMessageDialog(Component, Object, String, int, Icon)` | Show a one-button, modal dialog that gives the user some information. The arguments specify (in order) the parent component, message, title, message type, and icon for the dialog. See Creating and Showing Simple Dialogs for a discussion of the arguments and their effects.
> `int showOptionDialog(Component, Object, String, int, int, Icon, Object[], Object)` | Show a customized modal dialog. The arguments specify (in order) the parent component, message, title, option type, message type, icon, options, and initial value for the dialog. See Creating and Showing Simple Dialogs for a discussion of the arguments and their effects.
> `int showConfirmDialog(Component, Object) int showConfirmDialog(Component, Object, String, int) int showConfirmDialog(Component, Object, String, int, int) int showConfirmDialog(Component, Object, String, int, int, Icon)` | Show a modal dialog that asks the user a question. The arguments specify (in order) the parent component, message, title, option type, message type, and icon for the dialog. See Creating and Showing Simple Dialogs for a discussion of the arguments and their effects.
> `String showInputDialog(Object) String showInputDialog(Component, Object) String showInputDialog(Component, Object, String, int) String showInputDialog(Component, Object, String, int, Icon, Object[], Object)` | Show a modal dialog that prompts the user for input. The single-argument version specifies just the message, with the parent component assumed to be null. The arguments for the other versions specify (in order) the parent component, message, title, message type, icon, options, and initial value for the dialog. See Creating and Showing Simple Dialogs for a discussion of the arguments and their effects.
> `int showInternalMessageDialog(...) int showInternalOptionDialog(...) int showInternalConfirmDialog(...) String showInternalInputDialog(...)` | Implement a standard dialog as an internal frame. See the `JOptionPane` API documentation for the exact list of arguments.

> Methods for Using `JOptionPane`s Directly
> Method or Constructor | Purpose
> --- | ---
> `JOptionPane() JOptionPane(Object) JOptionPane(Object, int) JOptionPane(Object, int, int) JOptionPane(Object, int, int, Icon) JOptionPane(Object, int, int, Icon, Object[]) JOptionPane(Object, int, int, Icon, Object[], Object)` | Creates a `JOptionPane` instance. See Creating and Showing Simple Dialogs for a discussion of the arguments and their effects.
> `Frame getFrameForComponent(Component) JDesktopPane getDesktopPaneForComponent(Component)` | Handy `JOptionPane` class methods that find the frame or desktop pane, respectively, that the specified component is in.

> Frequently Used `JDialog` Constructors and Methods
> Method/Constructor | Purpose
> --- | ---
> `JDialog() JDialog(Frame) JDialog(Frame, boolean) JDialog(Frame, String) JDialog(Frame, String, boolean)` | Creates a `JDialog` instance. The `Frame` argument, if any, is the frame (usually a `JFrame` object) that the dialog depends on. Make the boolean argument `true` to specify a modal dialog, `false` or absent to specify a non-modal dialog. You can also specify the title of the dialog, using a string argument.
> `Container getContentPane() setContentPane(Container)` | Get and set the content pane, which is usually the container of all the dialog's components. See Using Top-Level Containers for more information.
> `int getDefaultCloseOperation() setDefaultCloseOperation(int)` | Get and set what happens when the user tries to close the dialog. Possible values: `DISPOSE_ON_CLOSE`, `DO_NOTHING_ON_CLOSE`, `HIDE_ON_CLOSE` (the default). See Responding to Window-Closing Events for more information.
> `void setLocationRelativeTo(Component)` | Centers the dialog over the specified component.

### Examples that Use Dialogs

> This table lists examples that use `JOptionPane` or `JDialog`. To find other examples that use dialogs, see the example lists for progress bars, color choosers, and file choosers.

> Example | Where Described | Notes
> --- | --- | ---
> `DialogDemo`, `CustomDialog` | This section | Creates many kinds of dialogs, using `JOptionPane` and `JDialog`.
> `Framework` | -- | Brings up a confirmation dialog when the user selects the Quit menu item.
> `ListDialog` | How to Use BoxLayout | Implements a modal dialog containing a scrolling list and two buttons. Doesn't use `JOptionPane`, except for the utility method `getFrameForComponent`.
> `TableDemo` | How to Use Tables | Brings up a warning dialog when the user types a non-number entry into a cell that must contain a number.

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