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 Object Component Container Window Dialog 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 Icon Message Input Value Option Buttons ● 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 Object s, often String s, 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 import javax.swing.*; public class DialogTest { public static void main(String[] args) { JOptionPane.showMessageDialog( null, "A CATASTROPHIC ERROR HAS OCCURRED."); System.exit(0); }

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... int response = JOptionPane.showConfirmDialog( null, "DO YOU WANT TO CONTINUE?"); if (response == JOptionPane.YES_OPTION) {... // user clicked YES } else if (response == JOptionPane.NO_OPTION) {... // user clicked NO } else {... // user clicked CANCEL }...

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)... int response = JOptionPane.showConfirmDialog( null, "DO YOU WANT TO CONTINUE?", "Continue Dialog", // Dialog title JOptionPane.OK_CANCEL_OPTION); if (response == JOptionPane.OK_OPTION) {... // user clicked OK } else {... // user clicked CANCEL }

Getting Textual Input ● showInputDialog can return a string that is input by the user ● There are many argument combinations. Here is the simplest:... String ssn = JOptionPane.showInputDialog( "ENTER YOUR SOCIAL SECURITY NUMBER");...

Getting List Selections Suppose you want a dialog to present the user with a list of possible selections: When the user clicks on the input area, a drop-down list appears:

Getting List Selections (cont'd) This requires a 7-argument call to showInputDialog :... String message = "Select your favorite cereal:"; String title = "Cereal Selection"; Object[] selectionValues = {"Corn Flakes", "Wheaties", "Cheerios"}; Object response = JOptionPane.showInputDialog( null, message, title, JOptionPane.QUESTION_MESSAGE, // message type null, // icon selectionValues, // selections selectionValues[0]); // initially // selected String favoriteCereal = (String)response;...