Java Reference
In-Depth Information
3. public void redo();
4. }
In the PIM, the location of an appointment will be used to implement an undoable command. An appointment
stores a description of an event, the people involved, the location, and the start and end time(s).
Example 2.6
Appointment.java
1. import java.util.Date;
2. public class Appointment{
3. private String reason;
4. private Contact[] contacts;
5. private Location location;
6. private Date startDate;
7. private Date endDate;
8.
9. public Appointment(String reason, Contact[] contacts, Location location, Date startDate,
Date endDate){
10. this.reason = reason;
11. this.contacts = contacts;
12. this.location = location;
13. this.startDate = startDate;
14. this.endDate = endDate;
15. }
16.
17. public String getReason(){ return reason; }
18. public Contact[] getContacts(){ return contacts; }
19. public Location getLocation(){ return location; }
20. public Date getStartDate(){ return startDate; }
21. public Date getEndDate(){ return endDate; }
22.
23. public void setLocation(Location location){ this.location = location; }
24.
25. public String toString(){
26. return "Appointment:" + "\n Reason: " + reason +
27. "\n Location: " + location + "\n Start: " +
28. startDate + "\n End: " + endDate + "\n";
29. }
30. }
The class
ChangeLocationCommand
implements the
UndoableCommand
interface and provides the behavior
required to change the location for an appointment.
Example 2.7
ChangeLocationCommand.java
1. public class ChangeLocationCommand implements UndoableCommand{
2. private Appointment appointment;
3. private Location oldLocation;
4. private Location newLocation;
5. private LocationEditor editor;
6.
7. public Appointment getAppointment(){ return appointment; }
8.
9. public void setAppointment(Appointment appointment){ this.appointment = appointment; }
10. public void setLocationEditor(LocationEditor locationEditor){ editor = locationEditor; }
11.
12. public void execute(){
13. oldLocation = appointment.getLocation();
14. newLocation = editor.getNewLocation();
15. appointment.setLocation(newLocation);
16. }
17. public void undo(){
18. appointment.setLocation(oldLocation);
19. }
20. public void redo(){
21. appointment.setLocation(newLocation);
22. }
23. }
The class provides the ability to change a location using the execute method. It provides undo behavior by storing
the previous value of the location and allowing a user to restore that value by calling the undo method. Finally, it
supports a redo method that enables users to restore the new location, if they happen to be very indecisive.
