CompSci 125 Lecture 19
GUI: Organizing classes, Mouse Events, KeyListener,
KeyEventDispatcher
Announcements
GUI Review
JFrame
§  Container
§  Title Bar includes the title
text, and the minimize,
maximize and close buttons
§  Content pane
§  Re-position the frame
§  Re-size the frame
http://docs.oracle.com/javase/6/docs/api/javax/swing/JFrame.html
Content Pane
§  Is the region in the JFrame where we can add/draw “stuff”
§  JFrame constructs the default pane as a JComponent
§  We can add other graphical components to it
§  Has a LayoutManager
§  getContentPane from the JFrame
§  setContentPane in the JFrame
§  add gui components to the content pane
http://docs.oracle.com/javase/tutorial/uiswing/components/toplevel.html
JPanel
§  Is a Container to which you may add other Components
§  May have a LayoutManager
§  Can be configured as double-buffered
§  You may add a JPanel to the content pane
§  Use setContentPane to replace the content pane with a JPanel
§  Implements a paintComponent(Graphics g) method
§  You may subclass a JPanel and override paintComponent
§  Then you can draw on the Graphics context
JLabel
§  Displays text string, an icon or both
§  “Write only” --- no user input possible
http://docs.oracle.com/javase/6/docs/api/javax/swing/JLabel.html
JButton
§  Displays a button
§  Our class implements the
ActionListener interface
§  Java calls ActionListener’s
actionPerformed method
when user clicks button
http://docs.oracle.com/javase/6/docs/api/javax/swing/JButton.html
ActionListener Interface
§  Our class includes “implements ActionListener” clause
§  Java ensures we implement the actionPerformed method
§  Java passes an ActionEvent parameter to actionPerformed
§  ActionEvent’s getSource method returns a reference to the
object (e.g. an instance of a JButton or JTextField) in which
the event occurred
JTextField
§  Displays text (like a JLabel)
§  Unlike a JLabel, user can enter text
§  Our class implements ActionListener
§  Java calls actionPerformed when user modifies text
§  ActionEvent’s getSource method identifies source of event
§  JTextField’s getText returns reference to user’s text String
§  Many, many methods!
http://docs.oracle.com/javase/6/docs/api/javax/swing/JTextField.html
paintComponent and the Graphics
Context
§  drawArc
§  drawImage
§  drawLine
§  drawOval
§  drawRect
§  drawString
§  fillArc
§  fillOval
§  fillRect
§  clearRect
§  getClipRect
§  setColor
§  setFont
§  more…
JCheckBox
§  Labeled stateful check box
§  Text label describes an attribute
§  Check box displays associated state (selected or not)
§  Clicking box toggles its associated state
§  Useful methods
§  JCheckBox(“Label Text String”)
§  isSelected()
§  Our class implements either ActionListener or ItemListener
interface
JRadioButton
§  Labeled stateful button
§  Text label describes an attribute
§  Button displays associated state (selected or not)
§  Clicking button toggles its associated state
§  Only one button in group selected at any time
§  Useful methods
§  JRadioButton(“Selected Button’s Text String”,true)
§  JRadioButton(“Unselected Button Text”)
§  isSelected()
§  Define a ButtonGroup and add each JRadioButton to it
§  Our class typically implements ActionListener interface
Layout Managers
§  BorderLayout: Five areas (north, south, east, west & center)
§  BoxLayout: Single row or column
§  CardLayout: Only one component visible at any one time.
Consider using JTabbedPane instead.
§  FlowLayout: Arranges components left-to-right, adding rows
as necessary
§  GridLayout: Grid of rows and columns
§  GridBagLayout: Like GridLayout, but components span cells
§  MigLayout: http://www.miglayout.com/QuickStart.pdf
Associating a Layout
Manager with the
Content Pane
§  A JFrame has an associated Content Pane
§  JFrame constructs the default Content Pane as a JComponent
§  But getContentPane returns a reference to a Container
§  Three ways to Associate Layout Manager with the Content Pane
1.  Replace the Layout Manager in the default content pane
2.  Replace default content pane with a JPanel having a Layout Manager
3.  Add a JPanel having a Layout Manager to the default content pane
http://docs.oracle.com/javase/tutorial/uiswing/components/toplevel.html#contentpane
1. Replace the Layout Manager in
the Default Content Pane
//Recommended approach unless you need to build!
//your own JPanel (to override paintComponent to!
//gain drawing access to the Graphics context)!
JFrame theFrame = new JFrame();!
.!
.!
.!
Container contentPane = theFrame.getContentPane();!
contentPane.setLayout(new FlowLayout());!
2. Replace the Default Content
Pane with your own JPanel
//Recommended approach if you need your own JPanel!
//to replace the default content pane!
JFrame theFrame = new JFrame();!
.!
.!
.!
JPanel contentPane = new JPanel(new FlowLayout());!
theFrame.setContentPane(contentPane);!
3. Overlay the Default Content
Pane with your own JPanel
//Your own JPanel covers the default content pane!
//which continues to exist!
JFrame theFrame = new JFrame();!
.!
.!
.!
JPanel contentPane = new JPanel(new FlowLayout());!
theFrame.getContentPane().add(contentPane);!
MouseListener
MouseListener
§  Java can notify our program of mouse activity
§  Our class implements the MouseListener interface
§  mouseClicked
§  mouseReleased
§  mouseEntered
§  mouseExited
KeyListener
KeyListener
§  Described in text. BUT…
§  “To fire keyboard events, a
component must have the
keyboard focus” --- http://
docs.oracle.com/javase/
tutorial/uiswing/events/
keylistener.html
§  THUS… your ap will quit
receiving KeyEvents when
some control grabs the “focus”
KeyEventDispatcher
KeyEventDispatcher
§  Want to catch *all* keyboard events in the JFrame
§  Java’s KeyboardFocusManager controls processing of KeyEvents
§  KeyBoardFocusManager registers KeyEventDispatchers (in a chain)
§  KeyBoardFocusManager dispatches KeyEvents to the chain before
sending them to the control having the current “focus”
§  Each KeyEventDispatcher in the chain has an opportunity to observe
the KeyEvent
§  AND… the responsibility to not inadvertently break the dispatcher
chain
§  http://docs.oracle.com/javase/7/docs/api/java/awt/KeyEventDispatcher.html
KeyEventDispatcher:
Register to Receive Key Events
§  Implement KeyEventDispatcher interface in your class
§  Find the KeyBoardFocusManager processor of all KeyEvents
KeyboardFocusManager mgr=
KeyboardFocusManager.getCurrentKeyboardFocusManager()!
§  Add instance of your class to Java’s chain of KeyEventDispatchers
mgr.addKeyEventDispatcher(myKeyEventDispatcher)!
§  Java will begin sending KeyEvents to your KeyEventDispatcher
§  http://docs.oracle.com/javase/1.4.2/docs/api/java/awt/KeyboardFocusManager.html
KeyEventDispatcher:
dispatchKeyEvent method
§  Java passes a single KeyEvent parameter to dispatchKeyEvent
§  Use KeyEvent’s getID method to determine the event type
§  You likely care about KeyEvent.KEY_PRESSED events
§  Use KeyEvent’s getKeyCode to see the actual key code
§  Return false to ensure Java finishes keyboard processing
§  http://docs.oracle.com/javase/7/docs/api/java/awt/KeyEventDispatcher.html