Full Code Examples - Applied Java Patterns - page 218

Factory Method
The following example uses the Factory Method pattern to produce an editor for the PIM. The PIM tracks a lot of
information, and there are many cases where users need an editor to create or modify data. The example uses
interfaces to improve the overall flexibility of the system.
The Editable interface defines a builder method, getEditor , which returns an ItemEditor interface. The
benefit is that any item can provide an editor for itself, producing an object that knows what parts of a business
object can change and how they can be changed. The only thing the user interface needs to do is use the
Editable interface to get an editor.
Example A.21 Editable.java
1. public interface Editable {
2. public ItemEditor getEditor();
3. }
The ItemEditor interface provides two methods: getGUI and commitChanges . The getGUI method is another
Factory Method—it returns a JComponent that provides a Swing GUI to edit the current item. This makes a very
flexible system; to add a new type of item, the user interface can remain the same, because it only uses the
Editable and the ItemEditor interfaces.
The JComponent returned by getGUI can have anything in it required to edit the item in the PIM. The user
interface can simply the acquired JComponent in its editor window and use the JComponent functionality to edit
the item. Since not everything in an application needs to be graphical, it could also be a good idea to include a
getUI method that would return an Object or some other nongraphical interface.
The second method, commitChanges , allows the UI to tell the editor that the user wants to finalize the changes he or
she has made.
Example A.22 ItemEditor.java
1. import javax.swing.JComponent;
2. public interface ItemEditor {
3. public JComponent getGUI();
4. public void commitChanges();
5. }
The following code shows the implementation for one of the PIM items, Contact . The Contact class defines two
attributes: the name of the person and their relationship with the user. These attributes provide a sample of some
of the information, which could be included in an entry in the PIM.
Example A.23 Contact.java
1. import java.awt.GridLayout;
2. import java.io.Serializable;
3. import javax.swing.JComponent;
4. import javax.swing.JLabel;
5. import javax.swing.JPanel;
6. import javax.swing.JTextField;
7.
8. public class Contact implements Editable, Serializable {
9. private String name;
10. private String relationship;
11.
12. public ItemEditor getEditor() {
13. return new ContactEditor();
14. }
15.
16. private class ContactEditor implements ItemEditor, Serializable {
17. private transient JPanel panel;
18. private transient JTextField nameField;
19. private transient JTextField relationField;
20.
21. public JComponent getGUI() {
22. if (panel == null) {
23. panel = new JPanel();
24. nameField = new JTextField(name);
25. relationField = new JTextField(relationship);
26. panel.setLayout(new GridLayout(2,2));
27. panel.add(new JLabel("Name:"));