Dialogues - An Introduction to Graphical User Interfaces with Java Swing - page 117

invisible. We check whether the dialogue is already defined by checking whether
the reference to it is null or not.

if (searchDialog == null )
{

searchDialog = new SearchDialog( this );
dataTransfer = new DataTransferObject();

}
The variables searchDialog and dataTransfer are previously declared, e.g.

private SearchDialog searchDialog;
private DataTransferObject dataTransfer;
but not instantiated using new .Wenow list the classes SearchDialog and Data-
TransferObject .

File: its/Dialogs/SearchDialog.java

package its.Dialogs; 1.

2.
3.

import java.awt.*;

import java.awt.event.*; 4.

import javax.swing.*; 5.

6.
7.

public class SearchDialog extends JDialog

{ 8.

9.

private JPanel mainPanel = new JPanel();

10.

private JTextField searchTextField = new JTextField();

11.

private JRadioButton yesButton = new JRadioButton("Yes");

12.

private JRadioButton noButton = new JRadioButton("No");

13.

private JButton searchButton = new JButton("Find");

14.

private JButton cancelButton = new JButton("Cancel");

15.

private DataTransferObject dataTransfer;

16.

private ButtonGroup group = new ButtonGroup();

17.
18.

public SearchDialog(Frame frame)

19.

{

20.

super (frame,"Search dialog", true );

21.
22.

JLabel questionS = new JLabel("search word:");

JLabel questionCS = new JLabel("case-sensitive?"); 23.

JLabel filler = new JLabel(); 24.

25.
26.

this .getContentPane().setLayout( new BorderLayout());

this .setLocation(300,300); 27.

this .getContentPane().add(mainPanel,BorderLayout.CENTER); 28.

29.