Looking for todays homework exercise

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Looking for todays homework exercise?

• Return to the Teaching Page of my home page and
  you will find it under
• Exercises and Handouts

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Event Handling
Graphical User Interface
Event
Event
Event
Widget
Registered Listeners Object A Object B Object C
Event Listeners or Event Handlers
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Creating Sending Events

• Events are not limited to GUI components, however
  they will be introduced and discussed in that
  context
• GUI components that can change state, generate
  events when a change occurs
• JButtons ActionEvent
• JTextField ActionEvent
• JLists ListSelectionEvent
• JCheckBox ItemEvent
• plus many, many more...
• All have a method which allows objects to
  register as an event listener
• addxxxListener(xxxListener x)

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Event Listeners/Handlers

• Event listeners are objects that implement the
  appropriate interface that will allow them to
  register with an object that generates events
• Ex JButtons
• JButton b new JButton(Button 1)
• Generate ActionEvents
• addActionListener(ActionListener a)
• Any object implementing the ActionListener
  interface can register with the JButton to be
  notified when it changes state (is pressed)
• public interface ActionListener
• void actionPerformed(ActionEvent e)
• public class MyObject implements ActionListener
• ...
• public void actionPerformed(ActionEvent e)
• System.out.println(Dont press the
  button!)
• MyObject mo new MyObject()

By implementing the ActionListener interface,
MyObject becomes an ActionListener
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Buttons

• import javax.swing.
• import java.awt.
• import java.awt.event.
• public class GuiTest
• public GuiTest()
• public static void main(String args)
• JFrame j new JFrame("Title")
• j.setSize(275, 170)
• Container c j.getContentPane()
• c.setLayout(new FlowLayout())
• JButton b new JButton("I Believe")
• b.addActionListener(new
  MyActionListener())
• c.add(b)
• JLabel lab new JLabel("Text and
  Graphics Label")
• c.add(lab)

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Adapters

• Interfaces require you to implement ALL of the
  methods
• As we saw with WindowEvent, there are seven
  methods associated with the WindowListener
  interface
• Cumbersome to implement all seven if we only want
  to handle one of the event types, i.e.,
  windowClosing()
• HenceAdapters
• abstract classes with empty methods
• public void windowClosing()
• simply provided as a convenience for implementing
  interfaces
• Use extend the abstract class and override
  desired methods
• How do we know if there is an adapter class
  associated with the interface?

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Buttons Revisted

• import javax.swing.
• import java.awt.
• import java.awt.event.
• public class GuiTest
• public GuiTest()
• public static void main(String args)
• JFrame j new JFrame("Title")
• j.setSize(275, 170)
• Container c j.getContentPane()
• c.setLayout(new FlowLayout())
• JButton b new JButton("I Believe")
• b.addActionListener(new
  MyActionListener())
• c.add(b)
• JLabel lab new JLabel("Text and
  Graphics Label")
• c.add(lab)

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Inner Classes

• import javax.swing.
• import java.awt.
• import java.awt.event.
• public class GuiTest extends JFrame
• private Container c
• public GuiTest(String t)
• super(t)
• setSize(275, 170)
• c getContentPane()
• c.setLayout(new FlowLayout())
• JButton b new JButton("I Believe")
• b.addActionListener(new
  MyActionListener())
• c.add(b)
• JLabel lab new JLabel("Text and
  Graphics Label")
• c.add(lab)
• setVisible(true)

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Exercise Handout

• See my homepage...More GUIs (12 Sep 05) under
  Exercises and Handouts
• Text Fields, Lists and Scroll Panes
• Adding additional function to your listeners
• Complete before tomorrows lab
• GUI reference Deitel Chapters 11 and 22