Page 703 - Introduction to Programming with Java: A Problem Solving Approach
P. 703
16.13 Dialog Boxes and the JOptionPane Class 669
import javax.swing.*;
public class HelloWithAFrame extends JFrame
{
}
// end class HelloWithAFrame
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public HelloWithAFrame()
{
setTitle("Hello");
setSize(400, 200);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setVisible(true);
// end HelloWithAFrame constructor
//***********************************************************
}
public static void main(String[] args)
{
HelloWithAFrame helloFrame = new HelloWithAFrame();
JOptionPane.showMessageDialog(helloFrame, "Hello, world!");
} // end main
Figure 16.10 HelloWithAFrame program and its output
Suppose you don’t want to bother with centering the dialog box within a particular container. In that case, use null for showMessageDialog’s container argument. That causes the dialog box to display in the center of the screen. For example, this code fragment generates a screen-centered dialog box:
JOptionPane.showMessageDialog(
null, "Before starting the installation,\n" +
"shut down all applications.");
By the way, it’s very common to use null for showMessageDialog’s container argument, probably more common than using a non-null value.
The JOptionPane class needs the javax.swing package. If you’ve imported the javax.swing package for the JFrame class already, there’s no need to import it again.
