Abstract Windowing Toolkit

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Abstract Windowing Toolkit

• Support for Graphical User Interface
• (Event-driven programming)

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• Batch Programs -gt Interactive Programs
• gt Graphical User Interfaces
• AWT
• Classes for creating GUIs organized as
  inheritance hierarchy.
• Define the structure (geometry) and the (default)
  behavior of the components
• (look and feel)
• Java-Components X-Widgets ActiveX-Controls

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AWT classes

• Component
• Basic Button, Choice, Checkbox, List, Canvas,
  Label, Scrollbar, etc
• Container Panel, ScrollPane, Window (Dialog,
  FileDialog, Frame), etc
• A container instance can hold component
  instances.
• LayoutManager FlowLayout, GridLayout,
  BorderLayout, CardLayout, etc
• Automatically manage the relative positioning of
  the component instances within a container
  instance.

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Structure Example

• import java.awt.
• public class DemoAwt extends Frame
• Label l new Label(Demo,
  Label.CENTER)
• Button b new Button(No Op)
• Checkbox c new Checkbox(WindowsNT)
• List li new List()
• constructor definition...
• public static void main (String argv)
• new DemoAwt()

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• ...
• DemoAwt()
• resize(200,300)
• setLayout(new FlowLayout())
• add(l)
• add(b)
• add(new TextField(TEXT)
  )
• add(c)
• add(li)
• li.addItem(Netcape)
• li.addItem(SUN)
• show()
• ...

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• ...
• DemoAwt()
• resize(250,150)
• setLayout(new BorderLayout())
• //
  default add(North,l)
• add(South,b)
• add(Center, new
  TextField(T))
• add(East,c)
• add(West,li)
• li.addItem(Netcape)
• li.addItem(SUN)
• show()
• ...

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Applet Version

• import java.awt.
• import java.applet.
• public class DemoAwt2 extends Applet
• init-code...
• public void start()
• show()
• public void stop()
• hide()

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• public void init()
• List li new List()
• li.addItem(Netcape)
• li.addItem(SUN)
• add(new Label(Demo))
• add(new Button(No Op))
• add(new Checkbox(WindowsNT))
• add(li)
• / ltapplet codeDemoAwt2 width250 height300gt
  
• lt/appletgt
• /

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Adding Behavior Event Model

• An event, such as mouse click, mouse motion,
  keyboard input, etc, associated with a component,
  can trigger a specific (event handler)
  method.
• Event instance fields
• id, target, x, y, when, key, modifier, etc.
• An event model specifies the protocol used to
  process/handle events.

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Java 1.0 Event Model

• Role of inheritance hierarchy
• To associate an event-handler with a component
  class, it must be sub-classed, to override
  the default handler.
• Role of containment hierarchy
• If an event-handler associated with the target
  returns true, then the event has been processed.
  Otherwise, the event is propagated to its
  container, for further processing.

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Problems

• Code Organization
• Proliferation of sub-classes.
• Complex switch in the top-level handleEvent().
• No clear separation between application code and
  the GUI.
• Efficiency
• No filtering of events. (Events delivered to a
  component even when an event is not handled.)

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Event model for Java 1.1 and Beans

• Delegation-based Model
• Event object propagated from source to listener
  by invoking an event-specific method on a
  listener.
• The listener implements an appropriate
  EventListener interface, and registers itself
  with the source.

event
source
listener
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• OO-Events
• java.awt.events.
• class java.util.EventObject
• interface java.util.EventListener
• Design Pattern
• event type EVevent
• interface EVListener
• source . addEVListener (target)
• source . setEVListener (target)
• target implements EVListener
• class EVAdapter
• Source can safely call any method in the
  interface on all (corresponding) listener targets.

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• import java.applet.
• import java.awt.
• import java.awt.event.
• public class Scribble11 extends Applet
• implements MouseListener, MouseMotionListener
  
• int oldX, oldY Graphics g
• init()...
• public void mousePressed(MouseEvent e)
• oldX e.getX() oldY e.getY()
  
• public void mouseReleased(MouseEvent e)
• public void mouseClicked(MouseEvent e)
• public void mouseEntered(MouseEvent e)
• public void mouseExited(MouseEvent e)
• public void mouseMoved(MouseEvent e)
• public void mouseDragged(MouseEvent e)
• g.drawLine( oldX, oldY, e.getX(), getY())

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• public void init()
• g getGraphics()
• addMouseListener(this)
• addMouseMotionListener(this)
• Button bgB new Button("Change
  Color")
• bgB.addActionListener(new ActionListener()
• public void actionPerformed(ActionEvent
  e)
• setBackground( newColor())
• repaint() )
• add(bgB)
• Button clearB new Button("Clear")
• clearB.addActionListener(new ActionListener()
• public void actionPerformed(ActionEvent e)
  
• Color c g.getColor() g.setColor(getBac
  kground())
• g.fillRect(0, 0, bounds().width,
  bounds().height)
• g.setColor(c)
• add(clearB)

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• import java.applet.
• import java.awt.
• import java.awt.event.
• public class Scribble22 extends Applet
• int oldX, oldY
• Graphics g
• public void init()
• g getGraphics()
• addMouseListener( new MouseAdapter()
  
• public void mousePressed(MouseEvent e)
• oldX e.getX() oldY
  e.getY()
  
• )
• addMouseMotionListener( new
  MouseMotionAdapter()
• public void mouseDragged(MouseEvent e)
  
• g.drawLine( oldX, oldY, e.getX(),
  e.getY())
• )

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• Button bgB new Button("Change Color")
• bgB.addActionListener(new ActionListener()
• public void actionPerformed(ActionEvent
  e)
• setBackground( newColor())
• repaint() )
• add(bgB)
• Button clearB new Button("Clear")
• clearB.addActionListener(new ActionListener()
• public void actionPerformed(ActionEvent e)
  
• Color c g.getColor() g.setColor(getBac
  kground())
• g.fillRect(0, 0, bounds().width,
  bounds().height)
• g.setColor(c)
• add(clearB)

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Advantages

• Flexible
• source-listener association dynamic.
• 1-1, 1-n, n-1, n-m source-listener combinations.
• Efficient
• Event-filtering Deliver only to registered
  listeners.
• Separation of Application and GUI code
• Enable (tool builders) run-time discovery of
  events that a component generates/observes.

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Low-level Event Handling

• One can subclass a component, to process events,
  by overriding the following methods
• protected void processEvent(AWTEvent)
• protected void processEV?Event(EV?Event)
• These are analogous to Java 1.0 handleEvent()
  and specific event-handlers respectively.
• It is necessary to enable delivery of events
  using
• protected void enableEvents(long eventsToEnable)
• Note one cannot mix 1.0 and 1.1 event
  models.

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• import java.applet.
• import java.awt.
• import java.awt.event.
• public class Scribble33 extends Applet
• int oldX, oldY
• Graphics g
• public void init()
• add( new Label("Scribbler Press 'c'
  to clear.") )
• g getGraphics()
• enableEvents(AWTEvent.MOUSE_EVENT_MASK
  
• AWTEvent.MOUSE_MOTION_EVE
  NT_MASK
• AWTEvent.KEY_EVENT_MASK)
  
• requestFocus()

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• public void processMouseEvent(MouseEvent e)
  
• if (e.getID() MouseEvent.MOUSE_PRES
  SED)
• oldX e.getX() oldY e.getY()
• else super.processMouseEvent(e)
• public void processMouseMotionEvent(MouseEvent
  e)
• if (e.getID() MouseEvent.MOUSE_DRAG
  GED)
• int x e.getX()
  int y e.getY()
• g.drawLine(oldX,oldY,x,y)
  
• oldX x oldY y
• else super.processMouseMotionEvent(e
  )

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• public void processKeyEvent(KeyEvent e)
• if ( (e.getID() KeyEvent.KEY_TYPED)
  
• (e.getKeyChar() 'c')
  )
• Color temp g.getColor()
• g.setColor(getBackground())
• g.fillRect(0, 0,
  getSize().width,
• 
  getSize().height)
• g.setColor(temp)
• else super.processKeyEvent(e)