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Event Driven Programming
Part 3 – Event Handling
Chapter 12
CS 2334
University of Oklahoma
Brian F. Veale
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Events
• All interaction with a GUI program is through
events
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Mouse clicks
Button presses
Text Entry
Menu selection
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Event Handling
• By default, some components appear to react
to certain interaction
– JScrollPanes will scroll
– JButtons will change color when clicked
• In order to write functional GUI programs we
must handle some events
• Java uses Listeners to manage event handling
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Listeners
• When we register an object as a Listener it
takes responsibility for certain events
– Only responsible for events from certain other
components
– Only responsible for a limited class of events
• Listeners are actually interfaces
– They are a group of methods that we agree to
implement
– Depending on the kind of Listener, we can have a
large number of methods to implement
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Common Listener Interfaces
• ActionListener
– Button being pressed
– Pressing return in a text field
– Selecting a menu item
• MouseListener
– Pressing a mouse button while over a certain component
• WindowListener
– Closing the main window
• KeyListener
– Pressing keys on the keyboard
• MenuListener
– Opening a menu
– Selecting a menu item
• More Listener Methods in the Java Tutorial – Listener API Table
• http://java.sun.com/docs/books/tutorial/uiswing/events/api.htm
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Implementing Event Handling
• Lets make it so that our GUI programs exit when we
close the window
– This can be annoying if not handled
– Without doing this, your windows disappear, but never exit
• This is going to be a window event connected to the
JFrame
• We’ll need to use a WindowListener
– WindowListener interface has 7 methods
• Every single one must be implemented
– The Adapter classes comes to our rescue, maybe
• You inherit from an Adapter class
• It contains skeletons for all corresponding Listener methods
– Difficulties
• Can only inherit from one class
• Not all Listeners have an Adapter
• Other option is to have skeleton methods for all the parts of the
interface that we won’t use
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Exiting a Program Upon Window Closing
• Which method of WindowListener should we use?
– void windowActivated(WindowEvent e)
• Invoked when the Window is set to be the active Window.
– void windowClosed(WindowEvent e)
• Invoked when a window has been closed as the result of calling
dispose on the window.
– void windowClosing(WindowEvent e)
• Invoked when the user attempts to close the window from the
window's system menu.
– void windowDeactivated(WindowEvent e)
• Invoked when a Window is no longer the active Window.
– void windowDeiconified(WindowEvent e)
• Invoked when a window is changed from a minimized to a normal
state.
– void windowIconified(WindowEvent e)
• Invoked when a window is changed from a normal to a minimized
state.
– void windowOpened(WindowEvent e)
• Invoked the first time a window is made visible.
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windowClosed() or windowClosing()
• void windowClosed(WindowEvent e)
• Invoked when a window has been closed as the result of
calling dispose on the window.
• void windowClosing(WindowEvent e)
• Invoked when the user attempts to close the window from
the window's system menu.
• Window.dispose()
– Releases all of the native screen resources used by the
Window.
– We will not work directly with instances of Window and
therefore cannot control when dispose() is called.
• windowClosing() seems like the best option
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Modifications to the Program
• frame.addWindowListener(this);
– The parameter is the name of the object that will handle
the event
– This line tells the component which object is responsible
for responding to this action
• Class Button extends WindowAdapter or Class Button
implements WindowListener
– The responding object must either extend the
WindowAdapter
• Only have to implement methods we’ll be using in
WindowListener
– or implement the WindowListener interface
• Have to write at least a skeleton for all methods in
WindowListener
• Write a method body for the responding object
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Demo Programs that use windowClosing()
• ButtonWithWindowClosing.java
• LabeledScrollingList3.java
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ActionListener
• Very high level event handler
– Can avoid some of the other types of event listeners
if we use ActionListener
• Very common type of listener
– Button presses
– Menu item selection
• Has a single method
– public void actionPerformed(ActionEvent e)
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Handling ActionEvents
• We can make a single object the ActionListener for
many other components
– Must distinguish who sent the event
– This data is stored in the ActionEvent object passed to
actionPerformed
– Methods for extracting event source info from
ActionEvent
• Object getSource()
– Returns the object that generated the call to actionPerformed
• String getActionCommand()
– Returns a string that contains the text of the object
– Can use setActionCommand to alter for an object
– Can be used for modal buttons
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Other methods in ActionEvent
• long getWhen()
– Gives us the time and date the event occurred
– Can convert to human-readable with Date class
• int getModifiers()
– Returns data on modifier keys pressed during event
(Ctrl, Shift, etc.)
• String paramString()
– Very useful for debugging
– Presents detailed information about event in textual
form
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ActionListener Demo
• ActionEvents.java
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WindowAdapter
• In ActionEvents.java, to use a WindowAdapter
to close the window, we had to create an inner
class.
• Inner classes are a reality of life in Java GUI
programs at times....
• But, is there a better way to close the window
when the user clicks on the window close
button?
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public void setDefaultCloseOperation(int operation)
• Sets the operation that will happen by default when the user initiates a
"close" on this frame.
– WindowConstants.DO_NOTHING_ON_CLOSE
• Don't do anything; require the program to handle the operation in the
windowClosing method of a registered WindowListener object.
– WindowConstants.HIDE_ON_CLOSE
• Automatically hide the frame after invoking any registered
WindowListener objects.
• Default action.
– WindowConstants.DISPOSE_ON_CLOSE
• Automatically hide and dispose the frame after invoking any registered
WindowListener objects.
– JFrame.EXIT_ON_CLOSE
• Exit the application using the System exit method. Use this only in
applications.
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Data Models
• We can develop a data model for our program
– Abstract Data Type
• Our ADT can be stored in a JList
• Demo 1:
– LabeledScrollingList4.java
– State.java
• Demo 2:
– StateListModel.java
– LabeledScrollingList5.java
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JList Mania
• The nomenclature for Swing JLists is somewhat
confusing
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–
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–
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JList
List
Vector
DefaultListModel
ArrayList
• Keeping these classes differentiated is
important
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Every JList has a data view
• data view = data model
• A JList is a GUI component
– It shows us a view of some data
• The items in the list
• We tell the JList what data to show when we construct it
• JLIst myList = new JList(Vector theData);
• This view is not inherently dynamic
– Call the constructor as above and then try to change
the vector’s data
– Won’t work too well (not at all)
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Making a dynamic JList
• Updating a JList
– myList.setListData(Vector theNewData);
• The JList will now show the current contents of the
theNewData vector
• Does this mean the Data model must be a Vector
– It could be a Vector
• Vector is part of the JCF
– Can be used as a List
» We can use Collections.sort()
» Can use all List methods
– It doesn’t have to be a Vector
• Can use another JCF List type
• Just make a method that returns a Vector of your List
contents
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Dynamic Lists Demo
• DynamicStateLists.java
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Clicking on a JList
• There are three ways to find out which item was clicked on in a
JList
– myJList.getSelectedIndex()
• This can work at any time
• Can be in ActionPerformed for a button
– ListSelectionListener
• Listener interface with only a single method
• public void valueChanged(ListSelectionEvent e)
• Called whenever the selected item changes
– MouseListener
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•
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Has seven methods
public void mouseClicked(MouseEvent e)
Add this listener to JList
Can detect single or double clicks
Call getSelectedIndex() to determine which item was clicked
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Beyond the JOptionPane
• JOptionPane was used in CS 1323 to create GUI based interfaces
• Very easy to use
– One line of code
– Don’t necessarily need to use with Event Listeners
• Lack some versatility
– Has only a single line of input
– Must have a long chain of these dialogs for object input
• Uses
– Short message dialogs
– Actions that only need confirmation
• Yes/No
• OK/Cancel
• http://java.sun.com/docs/books/tutorial/uiswin
g/components/dialog.html
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JDialog
• Swing component for Dialogs
– Used for modal or non-modal dialog windows
• Modal dialog: does not allow the user to interact with the
rest of the program while dialog is active
• Non-Modal dialog: user can interact with program while
dialog is active
– Construction
• Typically, we would write a class that inherits from JDialog
• JDialog myDialog = new JDialog (JFrame owner, boolean
modal)
– The owner frame is the JFrame from which the dialog is
shown
– Modal can be set either true or false
– Many other forms for the JDialog constructor
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How to design and use Dialogs
• This is a confusing topic for many students.
PersonEditDialog
Controller Pattern
dialog
person
person
name
email
etc.....
Person/Student/Professor
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Dialog Demos
• SimpleDialog Demo
– StudentDialog.java
– StudentEx.java / PersonEx.java
• PersonEditDialog Demo
– PersonEditDialog.java
– Student.java / Professor.java / Person.java
• PersonEditDialog with Exception Handling
– PersonEditDialogEx.java
– StudentEx.java / ProfessorEx.java /PersonEx.java
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