Design Pattern Guarded Suspension

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Design Pattern Guarded Suspension

• a concurrency pattern
• intent
• avoid the deadlock situation that can occur when
  a thread is about to execute an objects
  synchronized method and the state of the object
  prevents the method from executing to completion
• motivation
• a Queue class in a multiple thread environment
• call of pull when the Queue is empty (caller has
  to wait until an element is pushed to the queue)
• solution
• if the precondition is not fulfilled wait but
  release the lock (in Java use wait())

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Collaboration diagram
1a pull() concurrency guarded !isEmpty()
1b push() concurrency guarded
q Queue
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Example

• public class QueueltEgt
• private ArrayListltEgt data new ArrayListltEgt()
• synchronized public void push(E element)
• data.add(element)
• notify()
• synchronized public E pull()
• while (data.size() 0)
• try wait() catch (Exception e)
• E element data.removeFirst(0)
• return element

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Design Patter Producer-Consumer

• aka Pipe (just one Producer)
• a concurrency pattern
• intent
• coordination of asynchronous production and
  consumption of information or objects

Queue-produced objects
1
0..
Producer
Consumer
0..
consumer
1
queue
Consume-queued objects
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Example

• Class Queue as before (using the design pattern
  Guarded Suspension).
• public class Producer implements Runnable
• private Queue myQueue
• public Producer(Queue myQueue)
• this.myQueue myQueue
• public void run()
• myQueue.push(myData)

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Example (contd)

• public class Consumer implements Runnable
• private Queue myQueue
• public Consumer(Queue myQueue)
• this.myQueue myQueue
• public void run()
• myData myQueue.pull()

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GUI Programming

• graphical user interface
• human-computer interface
• replaces command-line interface
• interface builders
• Java AWT/Swing
• behavior is platform independent
• event-driven programming
• user in control
• user actions ? events
• program responds to events

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AWT and Swing

• AWT components are heavyweight
• associated with native components created by the
  underlying window system
• appearance determined by the window system
• different platforms different look
• Swing components are lightweight
• created by the JVM
• appearance determined by the JVM
• different platforms same look
• Composite design pattern

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AWT classes
Component
Container
Button
Canvas
Panel
Window
Checkbox
ScrollPane
Choice
Label
Frame
Dialog
List
Scrollbar
TextComponent
TextArea
TextField
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Swing classes
Container
Component
JComponent
JButton
JPanel
Window
JCombobox
JCheckbox
JLabel
Frame
Dialog
JList
JScrollbar
JFrame
JDialog
JTextComponent
JTextArea
JTextField
JWindow
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Component

• abstract class
• methods
• paint(Graphics g)
• repaint() calls paint
• setSize(int width, int height)
• setVisible(boolean b)
• requestFocus()
• validate()

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Container

• abstract class
• widget containers
• can contain containers
• layout
• LayoutManager
• methods
• add(Component comp)
• add(String name, Component comp)
• remove(Component comp)
• removeAll()
• setLayout(LayoutManager mgr)
• paint(Graphics g) // from Component
• should be overridden in order to draw
• all components of the container

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JComponent

• Swing version of Component
• abstract class
• adds additional functionality
• new methods
• Dimension getPreferredSize()
• Dimension getSize(Dimension rv)
• setPreferredSize(Dimension preferredSize)
• setEnabled(boolean enabled)

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JFrame

• top level window
• components
• menu bar
• content pane
• all layout etc.
• constructors
• JFrame()
• JFrame(String title)
• methods
• Container getContentPane()
• dispose() // from Window
• pack() // from Window
• setJMenuBar(JMenuBar menuBar)
• setResizable(boolean b) // from Frame
• setTitle(String title) // from Frame
• setDefaultCloseOperation(int operation)

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Layout managers

• each container has a layout manager
• handles the layout of the components contained in
  the container
• setLayout(lm) sets lm as the layout manager of
  this container

Container
LayoutManager
BorderLayout
CardLayout
FlowLayout
GridLayout
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Layout managers

• BorderLayout manager can manage five components,
• default layout manager for Frame, JFrame
• locations North, East, South, West, Center
• add(North, new Jbutton(Button 1)
• GridLayout manager creates a rectangular array of
  components
• each component occupies the same size portion of
  the screen
• new GridLayout(4,4,3,3)
• FlowLayout manager places components in rows left
  to right, top to bottom
• components need not to have the same size
• default manager for Panel
• CardLayout manager stacks components vertically
• only one component is visible at one time
• components can be named
• CardLayout lm new CardLayout()
• Panel p new Panel(lm)
• p.add(One, new Label(Number One))
• lm.show(p,One)

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Reaction Model

• reactive
• react to event as soon as it happens
• usually for buttons and menu selections
• write Listener and handle event
• used when view must change immediately
• completed data entry
• doing input validation
• reactive selections
• passive
• dont react to event when it happens
• wait until significant event (e.g. button press)
• access widget to get its state/contents
• usually for information entry
• text boxes
• selections

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Events

• caused by user actions
• event objects
• represent particular events
• carry further information
• event source objects
• register listeners
• send listeners events
• GUI widgets
• listeners
• receive/handle events
• listener interfaces

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Example - ActionEvent

• button presses cause ActionEvents
• ActionListeners handle ActionEvents
• actionPerformed
• getActionCommand
• JButton
• constructor
• addActionListener
• setActionCommand
• creating a button on the fly
• JButton button new JButton("Button")
• button.addActionListener(new ActionListener()
• public void actionPerformed (ActionEvent e)
• //do something
• )

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Example (cont.)

• using a private listener class
• JButton button new JButton("Button")
• button.addActionListener(new MyActionListener())
• ?
• private class MyActionListener implements
  ActionListener public void actionPerformed
  (ActionEvent e)
• //do something

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Example (cont.)

• combining the button and the listener in a new
  class
• JButton button new MyButton()
• ?
• private class MyButton extends JButton
• implements ActionListener
• public MyButton()
• super("Button")
• addActionListener(this)
• public void actionPerformed (ActionEvent e)
• //do something

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Example (cont.)

• a button to make a window invisible
• private class MyOKButton extends JButton
• implements ActionListener
• private JDialog parent
• public MyOKButton(JDialog parent)
• super("Ok")
• this.parent parent
• addActionListener(this)
• public void actionPerformed (ActionEvent e)
• parent.setVisible(false)

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Example (cont.)

• generic ButtonAdapter class
• abstract class ButtonAdapter extends JButton
• implements ActionListener
• public ButtonAdapter(String name)
• super(name)
• addActionListener(this)
• public void actionPerformed(ActionEvent e)
• pressed()
• public abstract void pressed()

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Listeners / Events /Adapters

• listener classes
• ActionListener
• ItemListener
• ListSelectionListener
• AdjustmentListener
• KeyListener
• MouseListener
• MouseWheelListener
• WindowListener
• ComponentListener
• ContainerListener
• event classes
• ActionEvent
• ItemEvent
• ListSelectionEvent
• AdjustmentEvent

• KeyEvent
• MouseEvent
• MouseWheelEvent
• WindowEvent
• ComponentEvent
• ContainerEvent
• adapter classes
• KeyAdapter
• MouseAdapter
• MouseMotionAdapter
• MouseInputAdapter
• WindowAdapter
• ComponentAdapter
• ContainerAdapter

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Event Hierarchy

• semantic events
• ActionEvent
• button click (incl. checkbox and radio button),
  menu selection combo box selection, enter in text
  area
• ItemEvent
• change of the state of an item, e.g., checkbox
  and radio box
• ListSelectionEvent
• list selections
• AdjustmentEvent
• scroll bar changes
• low level events
• KeyEvent
• MouseEvent
• MouseWheelEvent
• WindowEvent

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Listeners (cont.)

• handling window closing
• JFrame
• top level window
• window events
• WindowListener
• windowClosing
• addWindowListener(new WindowAdapter()
• public void windowClosing(WindowEvent e)
• setVisible(false)
• dispose()
• System.exit(0)
• )
• WindowAdapter
• null methods

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Listeners (cont.)

• private class MyMouseListener extends
  MouseAdapter
• public void mouseClicked (MouseEvent me)
• int x me.getX()
• int y me.getY()
• if (me.getButton() MouseEvent.BUTTON1)
• // action for left mouse button
• if (me.getButton() MouseEvent.BUTTON2)
• // action for middle mouse button
• if (me.getButton() MouseEvent.BUTTON3)
• // action for right mouse button