Outline

1
Outline

• JFrames
• Menus
• Event handling

2
Recap

• Basics of GUIs
• Swing components
• JComponent
• Various widgets
• Containers
• LayoutManagers
• Applets

3
JFrame Example
4
JFrames

• A JFrame is a container which uses a new window
  on-screen.
• Can have an associated menu, as shown in the
  example

5
JFrame Example code

• import javax.swing..
• import java.awt.
• public class JFrameTest
• public static void main(String args)
• JFrame frame new JFrame(Test Frame)
• frame.setSize(400, 400)
• JMenuBar menuBar new JMenuBar()
• JMenu fileMenu new JMenu(File)
• JMenuItem aboutMenuItem new
  JMenuItem(About)
• JMenuItem exitMenuItem new JMenuItem(Exit)
• fileMenu.add(aboutMenuItem)
• fileMenu.add(exitMenuItem)
• menuBar.add(fileMenu)

6
JFrame Code, cont

• JMenu editMenu new JMenu(Edit)
• JMenuItem cutMenuItem new JMenuItem(Cut)
• JMenuItem copyMenuItem new JMenuItem(Copy)
• JMenuItem pasteMenuItem new
  JMenuItem(Paste)
• editMenu.add(cutMenuItem)
• editMenu.add(copyMenuItem)
• editMenu.add(pasteMenuItem)
• menuBar.add(editMenu)
• frame.setJMenuBar(menuBar)
• JButton button1 new JButton(Cut)
• JButton button2 new JButton(Copy)
• JButton button3 new JButton(Paste)

7
JFrame Code, cont

• frame.getContentPane().setLayout(new
  FlowLayout())
• frame.getContentPane().add(button1)
• frame.getContentPane().add(button2)
• frame.getContentPane().add(button3)
• frame.setVisible(true)
• Components must be added to the content pane of
  the frame (use getContentPane() to access it)
• setVisible makes the frame (in)visible

8
JFrame Use

• A typical application uses a number of different
  JFrames over the course of execution
• Usually, all frames get created at start-up, and
  those not used initially are set invisible
• As buttons are pressed and menu items selected,
  different frames are set invisible and visible

9
Events

• Some sort of input (usually generated by the
  user, but possibly by network or another program)
• E.g.,
• pressing a key
• clicking or moving the mouse
• resizing or closing a window
• etc

10
Event Listeners

• The Swing components have built-in functionality
  to determine when particular events occur
• Applications generally need to respond to certain
  events e.g., exit the program if the quit button
  is pressed
• Register Event Listeners with components to get a
  notification when an event occurs

11
Event Listeners, Conceptually
Hey dude, I have been clicked on !
OK, I got you, Ill take it from here.
Component
Event Listener
12
Event Handling

• Register event handler with component
• Otherwise, component just ignores events, since
  it doesnt know anyone is interested
• Write event handling code
• What needs to be done on each event is
  application-specific, so you have to tell the
  computer what to do when a particular event
  occurs (by writing code to do it)
• Note more than one event handler can be
  registered for a given component

13
ActionEvent/Listener

• ActionEvent occurs when user
• Clicks on a button
• Presses ltENTERgt in a text field
• Generally, when a full action (with respect to a
  certain widget) is performed
• ActionListener is an interface that can be used
  to listen to ActionEvents.

14
Creating an ActionListener

• Create the component and add it to some
  containerJButton button new JButton(Quit)co
  ntainer.add(button)
• Register action event handler with the
  componentQuitEventHandler handler new
  QuitEventHandler()button.addActionListener(han
  dler)

15
Creating an ActionListener, cont

• Write a handler for the action event
• public class QuitEventHandler implements
  ActionListener
• public void actionPerformed(ActionEvent e)
• System.out.println(Quit button pressed! Bye
  bye)
• System.exit(0)
• In most cases, the parameter (the event object)
  can be ignored. It contains information such as
  event time, keyboard modifiers, etc.

16
Mouse Events

• Mouse enter/exits a window
• A mouse button is pressed or released
• A mouse button is clicked (a press and release)
• A mouse button is double-clicked
• MouseListener contains a method to handle each of
  these events

17
Creating a Mouse Handler

• Create a new component, add it to the
  containerJPanel panel new JPanel()container.a
  dd(panel)
• Register a mouse event handler on the
  componentMouseEventHandler handler new
  MouseEventHandler()panel.addMouseListener(handle
  r)

18
Mouse Listener Example, cont

• Write a mouse event handler
• public class MouseEventHandler implements
  MouseListener
• public void mouseClicked(MouseEvent e)
  System.out.println(Clicked!)
• public void mousePressed(MouseEvent e)
  System.out.println(Pressed!)
• public void mouseReleased(MouseEvent e)
  System.out.println(Released!)
• public void mouseEntered(MouseEvent e)
  System.out.println(Entered!)
• public void mouseExited(MouseEvent e)
  System.out.println(Exited!)

19
Window Listeners

• Window is opened
• Window is activated/de-activated (receives/loses
  focus)
• Window is iconified/de-iconified
• Window is closing

20
Key Listeners

• Key is pressed
• Key is released
• Key is typed (press and release)
• The key event includes which key was pressed

21
Summary of Important Events

• ActionEvent
• button click, text field enter, list double-click
• MouseEvent
• click, enter, exit, press, release
• WindowEvent
• open, close, de/iconify, de/activate
• Key Event - press, release, type a key

22
Event Adapters

• Often one only cares about one or two events in
  any particular listener interface
• E.g., most applications only care about window
  closing (so they can properly clean up and exit)
  from WindowListener
• Adapters implement corresponding listener
  interfaces with empty method bodies

23
Adapters, contd

• Allows us to subclass the adapter, and only
  implement the methods we care about
• Otherwise, wed need to write empty method bodies
  ourselves to fully implement the listener
  interfaces
• Every listener has a corresponding adapter
• e.g., MouseListener has MouseAdapter, KeyListener
  has KeyAdapter, etc.

24
Adapter Example

• public class QuitKeyListener extends KeyAdapter
• public void keyTyped(KeyEvent e)
• if ( e.getKeyChar() q e.getKeyChar()
  Q )
• System.exit(0)
• // No need to have empty keyPressed or
  keyReleased definitions //inherited from
  KeyAdapter

25
Event Handling Example

• SwingAction.java (available on the lecture
  notes page on the course website.)

26
Summary

• Use JFrames to create your own windows and JMenus
  to piece menus together
• Use Event Listeners to catch user input events,
  and cause your applications to react to the user
• Use Adapters if only a couple of events from a
  given listener interface are desired

27
Next Class

• Exception Handling