Creating and Using Dialogs

• A dialog is a box that pops up and prompts the user for a value or informs them of something
• One way: directly create objects of type JDialog

Using JDialog

• JDialog, like JFrame, JWindow, and JApplet, uses a content pane to organize its contents
• If you create a JDialog directly, you are responsible for:
  • Laying out the dialog components (BorderLayout by default):
    • Messages and Icons
    • Input areas and Buttons (Yes, No, Ok, Cancel, etc.)
  • Adding listeners to the dialog components
  • Showing and hiding the dialog when appropriate

Another Way: JOptionPane

• The JOptionPane class has a number of static methods that do the work of creating, laying out, and adding listeners for dialogs that perform standard functions
• The methods are of the form showXXXDialog where XXX is:
  • Message: Tell the user about something that has happened
  • Confirm: Ask a confirming question, like yes/no/cancel
  • Input: Prompt for some input
  • Option: Combination of the above

General Dialog Layout

• Note: the dialogs created by the JOptionPane class are modal, that is, processing is blocked until user interaction is complete

Arguments Accepted by showXXXDialog Methods

• Parent component: used to position dialog; if null then dialog is centered on screen
• Message: a descriptive message to be displayed in the dialog box, often a String
• Message type: coded integer specifying the style of the message:
  • JOptionPane.ERROR_MESSAGE
  • JOptionPane.INFORMATION_MESSAGE
  • JOptionPane.QUESTION_MESSAGE
  • JOptionPane.WARNING_MESSAGE
  • JOptionPane.PLAIN_MESSAGE

Arguments Accepted by showXXXDialog Methods (cont'd)

• Title: title to appear on dialog's title bar
• Button options: coded integer defining the set of available response buttons:
  • JOptionPane.OK_CANCEL_OPTION
  • JOptionPane.YES_NO_OPTION
  • JOptionPane.YES_NO_CANCEL_OPTION
  • JOptionPane.DEFAULT_OPTION
• Icon: icon to be displayed by message. If null, a default is used depending on Message type and Look-and-Feel

Arguments Accepted by showXXXDialog Methods (cont'd)

• Selection values: an array of Objects, often Strings, to be selected from when getting input from user
• Initial selection value: value from Selection values to be selected by default

An Example Dialog Task

• Put up a dialog that:
  • Displays an icon indicating this is a dialog that is transmitting information
  • Displays the message ''A CATASTROPHIC ERROR HAS OCCURRED''
  • Displays a single button labeled ''OK''
  • Adds a listener to the button that causes the dialog to disappear when the button is clicked, allowing processing to continue

A Simple Message Dialog

Notes On The Example

• As a static method, showMessageDialog must be fully qualified by the class name
• As a void method, showMessageDialog is called for side effect
• The first argument is the dialog's parent component. If null, the dialog is centered on the screen
• The second argument is an Object to be displayed, often a String
• Output:

Dialogs That Ask Questions

• The showConfirmDialog method can present more than one button, from among Yes, No, OK, and Cancel
• A symbolic integer is returned indicating which button was clicked:
  • JOptionPane.CANCEL_OPTION
  • JOptionPane.YES_OPTION
  • JOptionPane.NO_OPTION
  • JOptionPane.OK_OPTION
• Use this value to determine the course of action to take after interaction with the user

showConfirmDialog Example

Changing the Dialog Title and Buttons

• All showXXXDialog methods have multiple versions allowing different combinations of arguments
• Suppose you want only the OK and Cancel buttons, and a non-default dialog title:

Changing the Dialog Title and Buttons (cont'd)

Getting Textual Input

• showInputDialog can return a string that is input by the user
• There are many argument combinations. Here is the simplest:

Getting List Selections

Getting List Selections (cont'd)