Learning Java

Dialogs

A dialog is another standard feature of user interfaces. Dialogs are frequently used to present information to the user (“Your fruit salad is ready.”) or to ask a question (“Shall I bring the car around?”). Dialogs are used so commonly in GUI applications that Swing includes a handy set of pre-built dialogs. These are accessible from static methods in the JOptionPane class. Many variations are possible; JOptionPane groups them into four basic types:

message dialog

Displays a message to the user, usually accompanied by an OK button.

confirmation dialog

Ask a question and displays answer buttons, usually Yes, No, and Cancel.

input dialog

Asks the user to type in a string.

option dialogs

The most general type—you pass it your own components, which are displayed in the dialog.

A confirmation dialog is shown in Figure 14.10.

Figure 14-10. Using a confirmation dialog

Let’s look at examples of each kind of dialog. The following code produces a message dialog:

JOptionPane.showMessageDialog(f, "You have mail.");

The first parameter to showMessageDialog( ) is the parent component (in this case f, an existing JFrame). The dialog will be centered on the parent component. If you pass null for the parent component, the dialog is centered in your screen. The dialogs that JOptionPane displays are modal , which means they block other input to your application while they are showing.

Here’s a slightly ...