Event Handling

1
Week Four

• Event Handling
• Inner classes
• Event Handling and Inner Classes
• GUI Programming
• Threads and Web Servers

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Event Handling

• Used by the Abstract Window Toolkit (AWT) for
  basic GUI
• programming
  Java 1.0
• Used by Swing -- Better components than
  AWT Java 2
• Used by JavaBeans -- reusable software
  components, like
• Visual
  Basic, that can be manipulated
• in a
  builder tool

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Babysitting
A baby in the home needs attention. Many events
surrounding the baby are not easily
ignored. Events can be of different types.
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One possible source of events
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Babysitting
Before responding to an event, a babysitter
typically takes note of the source and the type
of event.
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Babysitting
Handler
Event type
Event source
The sitter needs to know both the event type and
the event source.
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Event Handling
The window manager software may generate hundreds
of different events. Examples include mouse
clicks, mouse movements, key strokes, and timer
ticks. A programmer is typically interested in a
small subset of all of the possible events that
may occur.
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Events and Event Objects

• Since events may be of different types but still
  exhibit some
• shared traits (inheritance) Java represents the
  event classes
• in a hierarchy.
• The root class is called java.util.EventObject.
  The only common
• feature shared by all events is a source
  object. So we find the
• following method in the EventObject class
• public Object
  getSource()

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Object
Some classes and methods in the event hierarchy.
EventObject
AWTEvent
ActionEvent
ComponentEvent
String getActionCommand()
WindowEvent
InputEvent
boolean isAltDown()
Window getWindow()
MouseEvent
KeyEvent
int getX()
char getKeyChar()
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Event handling usually involves three types of
objects

• Objects are used to hold and report on
  information about the event.
• Objects are typically the source of events.
• Objects, called listeners, are used to handle
  events.

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Example
A mouse object
An event object that describes, say, the x and y
coordinate of where the mouse was clicked
Event data and methods
Event Source
Listener
The listener object has methods that are called
for particular events
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Example
A mouse object
An event object that describes, say, the x and y
coordinate of where the mouse was clicked
Implements MouseListener
A mouse object must be told who its listener is.
The listener object has methods that are called
for particular events
The event object is sent to a listener method
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The Listener
There are different types of Listeners. MouseList
eners WindowListeners ScrollBarListeners Etc.. Th
ese Listeners are interfaces. Remember what an
interface provides? If class X implements an
interface then class X promises to provide (at
least) the methods declared in the interface.
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Some of the Listener Hierarchy
EventListener
KeyListener
ActionListener
MouseListener
abstract void actionPerformed(ActionEvent e)
abstract void mouseClicked(MouseEvent e)
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A Listener Interface
public interface MouseListener void
mouseClicked(MouseEvent e) void
mouseEntered(MouseEvent e) void
mouseExited(MouseEvent e) void
mouseReleased(MouseEvent e)
//What does it mean if I claim that I implement
this interface?
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An Example
// MouseSpyApplet.java import java.applet.Applet
import java.awt.event.MouseEvent import
java.awt.event.MouseListener
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class MouseSpy implements MouseListener public
void mouseClicked(MouseEvent event)
System.out.println("Mouse clicked. x "
event.getX() " y " event.getY())
public void mouseEntered(MouseEvent event)
System.out.println("Mouse entered. x "
event.getX() " y " event.getY())
public void mouseExited(MouseEvent event)
System.out.println("Mouse exited. x "
event.getX() " y " event.getY())
public void mousePressed(MouseEvent event)
System.out.println("Mouse pressed. x "
event.getX() " y " event.getY())
public void mouseReleased(MouseEvent event)
System.out.println("Mouse released. x "
event.getX() " y " event.getY())

I have to provide ALL of these methods!!
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public class MouseSpyApplet extends Applet
public MouseSpyApplet() MouseSpy listener
new MouseSpy() addMouseListener(listener)

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Java Applets need an HTML file.
lthtmlgt ltheadgt lt/bodygt lt/headgt ltBgtSpying on the
mouselt/bgtltpgt ltapplet code"MouseSpyApplet.class"
width400 height200gt lt/appletgt lt/htmlgt
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Another approach
Suppose a friendly sole created this
class public class MouseAdapter implements
MouseListener void mouseClicked(MouseEvent
e) void mouseEntered(MouseEvent e)
void mouseExited(MouseEvent e) void
mouseReleased(MouseEvent e) Now, suppose I
extend this class. What must I provide?
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Only those methods that I am interested in. The
other methods, when called, do nothing. Well
visit this issue again later.
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Inner Classes

• Nested Top Level Classes (not inner)
• Member Classes
• Local Classes
• Anonymous Classes

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Nested Top Level Class

• Nested top-level classes are not inner classes.
• Use as a convenient way to group related classes
• Since the class must be static and has no 'this'
  pointer, it
• has no access to the instance data of objects
  for its
• enclosing class.
• It behaves just like a 'normal' class or
  interface.

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//NestedTopLevelExample.java class Top
int i,j static class SomeClass //
static makes it top-level nested
int k SomeClass()
System.out.println("Constructi
ng SomeClass")
void foo() System.out.println("Hello")
Top()
System.out.println("Constructing a Top object")

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public class NestedTopLevelExample
public static void main(String args)
Top myTop new Top()
Top.SomeClass myObject new Top.SomeClass()
myObject.foo()
Output Constructing a Top object Constructing
SomeClass Hello
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Member Classes

• Member classes (there is no such thing as a
  'member
• interface)
• This inner class (it's not a top-level class)
  has no static
• keyword and can access the members of each
  object of
• its outer class.
• The class 'appears in every instance'.

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• The parent class must declare an instance of an
  inner class, before it can invoke the inner
  class methods, assign to data fields (including
  private ones), and so on.
• Unlike nested top-level classes, inner classes
  are not directly part of a package and are not
  visible outside the class in which they are
  nested.
• Inner classes are often used for GUI event
  handlers.

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// MemberClassExample.java class Top int
i 33 public class SomeClass
// access the outer object's state.
private int k i
SomeClass()
System.out.println("Constructing SomeClass")
void foo()
System.out.println("Hello")
Top() System.out.println("Cons
tructing a Top object")
SomeClass sc new SomeClass()
System.out.println(sc.k)
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public class MemberClassExample public
static void main(String args) Top
myObject new Top() //
OUTPUT Constructing a Top object Constructing
SomeClass 33
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Local Classes

• A Local class is an inner class. Typically, a
  local class
• is declared within a method. It is not a member
  of an
• enclosing class. It is visible only within the
  block.
• These classes are used primarily as "adapter
  classes".
• For example, a block of code that creates a
  Button object
• could use a local class to define a simple
  implementation
• of the ActionListener Interface. Then it could
  instantiate
• this simple implementation and pass the
  resulting object
• to the button's ActionListener method, thereby
  connecting
• the button to the "callback" code that is
  executed when
• the button is pressed.

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// Local Class example class Top int i
33 Top()
System.out.println("Constructing a Top object")
// define a class within a
method class Wow
int t Wow()
System.out.println("Building a Wow")
i 8
t 9
Wow h new Wow()
System.out.println(" h.t "
h.t) System.out.println(" i
" i)
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public class LocalExample public
static void main(String args) Top
myObject new Top() //
OUTPUT Constructing a Top object Building a Wow
h.t 9 i 8
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Anonymous Classes

• An anonymous class is refinement of inner
  classes.
• It allows you to combine the definition of the
  class
• with the instance allocation.
• Since it is instantiated in the same expression
  that defines
• it, it can only be instantiated once. This is
  very similar to
• local classes.
• When writing a simple adapter class, the choice
  between
• a named local class and an unnamed anonymous
  class
• typically comes down to a matter of style and
  code clarity,
• rather than any difference in functionality.
• The new class can't have a constructor.

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// Anonymous.java interface SmallClass
public void foo() class Top int i
33 void someMethod(SmallClass s)
s.foo() void anotherMethod()
someMethod(new SmallClass()
public void foo()
System.out.println(
"Really fun")
)
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Top()
System.out.println("Constructing a Top object")
someMethod(new SmallClass()
public void foo()
System.out.println("
Strange but fun")
)

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public class Anonymous public static
void main(String args) // We
can't create interface objects //
error SmallClass s new SmallClass()
Top myObject new Top()
myObject.anotherMethod() //
OUTPUT Constructing a Top object Strange but
fun Really fun
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Event Handling and Inner Classes

• register

Source Object
Listener Object
Event object
fire events
After the listener object registers itself with
the source object, the source object calls a
method found in the listener object and passes an
object that describes the event.
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Event Handling
Suppose we have a Button object Button b new
Button() We must determine what events a
particular component generates. A Button
component may generate an ActionEvent object.
Button b
ActionEvent Object
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Implementing a Listener

• We need an object that will listen for the
  ActionEvent.
• We implement the ActionListener class (this class
  listens
• for ActionEvents from buttons, menus, etc.) and
  override
• its actionPerformed method.

class BabySitter implements ActionListener
public void actionPerformed(ActionEvent e)
// handle the event object e in some
way
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Create a BabySitter object
BabySitter sitter new BabySitter()
sitter
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Registering The Listener

• We want to listen for the ActionEvent object
  coming from the button.
• So, we tell the button what object will listen
  for the ActionEvent object
• b.addActionListener(sitter)

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The button and its listener

addActionListener
Button Object
Sitter Object
The button calls the actionPerformed() method of
the sitter object and passes an ActionEvent
object as a parameter
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Once again but with a window
Hit the X and the program exits
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Create a WindowCloseSitter Class
import javax.swing. import java.awt.event. p
ublic class CloseDemo public static void
main(String args) JFrame f new
JFrame("Example") f.setSize(400,100)
f.setVisible(true) WindowCloseSitter h
new WindowCloseSitter()
f.addWindowListener(h)
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But we have to implement ALL of the
functions !!
class WindowCloseSitter implements WindowListener
public void windowClosing(WindowEvent e)
System.exit(0) public
void windowClosed(WindowEvent e) public
void windowOpened(WindowEvent e) public
void windowIconified(WindowEvent e)
public void windowDeiconified(WindowEvent e)
public void windowActivated(WindowEvent e)
public void windowDeactivated(WindowEvent e)

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Java Provides Adapter Classes

• ComponentAdapter
• MouseMotionAdapter
• WidowAdapter
• ContainerAdapter
• MouseAdapter
• FocusAdapter
• KeyAdapter

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The WindowAdapter class
public abstract class WindowAdapter implements
WindowListener public void
windowClosing(WindowEvent e) public void
windowClosed(WindowEvent e) public void
windowOpened(WindowEvent e) public void
windowIconified(WindowEvent e) public
void windowDeiconified(WindowEvent e)
public void windowActivated(WindowEvent e)
public void windowDeactivated(WindowEvent e)

A built in class -- we already have the empty
bodies!!
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The Window again
import javax.swing. import java.awt.event. pub
lic class CloseDemo2 extends WindowAdapter
public static void main(String args)
JFrame f new JFrame("Example")
f.setSize(400,100) f.setVisible(true)
f.addWindowListener(new CloseDemo2())
public void windowClosing(WindowEvent
e) System.exit(0)
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Again with anonymous classes
import javax.swing. import java.awt.event. pub
lic class CloseDemo3 public static void
main(String args) JFrame f new
JFrame("Example") f.setSize(400,100)
f.setVisible(true) f.addWindowListener(
new WindowAdapter()
public void windowClosing(WindowEvent e)
System.exit(0)
)
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GUI Programming with threads
Java GUI programming and Java Threads GUI
example taken from Computing Concepts with Java
2 by Cay Horstmann Thread examples taken from
The Java Programming Language By Arnold and
Gosling and from Cay Horstmanns Core Java 2
Advanced
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Frame Windows
A Frame window has a border and a title bar A
Frame window has an addWindowListener method. We
can use this method to add listeners to our frame
window.
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An example
javax means Java standard extension
import javax.swing. import java.awt.event. pu
blic class InternetFrameExample public
static void main(String args) JFrame
f new InternetFrame("Example")
f.setTitle("Internet browser") f.show()

Tell the window manager to display the frame.
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class InternetFrame extends JFrame public
InternetFrame(String s)
setSize(300,300)
WindowCloser listener new WindowCloser()
addWindowListener(listener) private
class WindowCloser extends WindowAdapter
public void windowClosing(WindowEvent e)
System.exit(0)

Add the handler
windowOpened() widowClosed() windowClosing()

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(No Transcript)
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Adding User Interface Components to a Frame

• Do not draw directly on the surface of a frame.
• Frames have been designed to arrange user
  interface components.
• User interface components are such things as
  buttons, menus,
• scroll bars, and so on.
• If you want to draw on a frame, draw on a
  separate component and
• then add that component to the frame. The Swing
  UI toolkit
• provides the Jpanel class for this purpose.

56
Drawing on a JPanel
To draw on a Jpanel you override the
paintComponent method. Make sure that from
within your paintComponent method you call
super.paintComponent() so that the superclass
method paintComponent has a chance to erase the
existing contents, redraw the borders and
decorations, etc.
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Adding the Panel to the JFrame

• The surface of a Swing frame is covered with four
  panes.
• Each of these four has a purpose.
• We are interested in getting access to the
• JFrames content pane.
• So, call the getContentPane on the JFrame.
• This call returns a Container object.
• Add your Panel object to the content pane
  Container.

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Adding a Panel to a JFrame
x getContentPane (a contentPane
holds components for display).
JFrame
getContentPane()
x refers to a Container (may contain other
components)
c a Panel or some other component.
Add c to x using xs layout manager (a content
pane uses border layout)
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Adding a JTextfield to the JFrame
JFrame
class MyFrame extends JFRAME private
JTextField textField public MyFrame()
Container cp getContentPane()
textField new JTextField()
cp.add(textField, South)
getContentPane()
cp
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We may want to add a listener to the TextField
JFrame
Class MyFrame extends JFRAME private
JTextField textField public myFrame()
Container cp getContentPane()
textField new JTextField()
cp.add(textField, South)
textField.addActionListener( new
TextFieldListener())
getContentPane()
cp
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Output first! -- user enters number of eggs and
we draw them
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Strategy

• Think about
• What do we want on the screen?
• What events should we listen for?
• What should we do when those events occur?
• What processing will we do when user input
  arrives?
• What object has responsibilities for what
  activities?

• Think about
• The has-a relationship,e.g., the Jframes
  ContentPane has-a
• Panel and a TextField.
• The is-a relationship,e.g., The
  TextFieldListener is-an
• actionListener.

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// Example // Eggs.java import
java.awt.Container import java.awt.Graphics impo
rt java.awt.Graphics2D import java.awt.event.Acti
onEvent import java.awt.event.ActionListener imp
ort java.awt.event.WindowAdapter import
java.awt.event.WindowEvent import
java.awt.geom.Ellipse2D import
java.util.Random import javax.swing.JFrame impor
t javax.swing.JPanel import javax.swing.JTextFiel
d
We need classes from the awt, util, and
swing packages.
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public class Eggs public static void
main(String args) EggFrame frame new
EggFrame() frame.setTitle("Enter number of
eggs") frame.show()
This thread is done after creating a frame
and starting up the frame thread.
A frame now exists and is running.
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The EggFrame Constructor

• Set the size of the frame
• Add a listener to listen for the stop event
• Create a JPanel object to draw on and a
  JTextField object to interact with the user via
  the keyboard
• Add a listener for the JTextField
• Add the Jpanel and the JTextField to the
• contentPane container.

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class EggFrame extends JFrame private
JTextField textField private EggPanel
panel public EggFrame() final
int DEFAULT_FRAME_WIDTH 300 final int
DEFAULT_FRAME_HEIGHT 300
setSize(DEFAULT_FRAME_WIDTH,
DEFAULT_FRAME_HEIGHT)
addWindowListener(new WindowCloser())
panel new EggPanel() textField new
JTextField() textField.addActionListener(n
ew TextFieldListener()) Container
contentPane getContentPane()
contentPane.add(panel, "Center")
contentPane.add(textField, "South")
A listener for the jframe window
A textField listener
As before
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Event driven programming
The constructor will be called from our main
thread. The other thread operates
asynchronously. What do we mean by asynchronous
execution? Who is running the show? Dont
programs run sequentially? We have to think
differently.
68
The TextField
The TextField object will call us when it
detects an event. We dont read the input. We
set up a babysitter to respond. The TextField
object sends us an event object.
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// Use an inner class to listen on
the text field private class
TextFieldListener implements ActionListener
public void actionPerformed(Action
Event event)
String input textField.getText()
panel.setEggCount(Integer.parseInt(input))
textField.setText("")

• We do two things when we
• have a textfield event.
• Get the data
• Tell the panel the number
• of eggs to display

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// Use an inner class to listen on
the text field private class
TextFieldListener implements ActionListener
public void actionPerformed(Action
Event event)
String input textField.getText()
panel.setEggCount(Integer.parseInt(input))
textField.setText("")

Note how handy the inner class is. Both panel and
textField are available. What if the listener
were not an object of an inner class. how would
it get access to these variables? We cant just
pass the variables on the call because we dont
make the call.
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private class WindowCloser extends
WindowAdapter public void
windowClosing(WindowEvent event)
System.exit(0)
This is how we respond when the close signal is
received. system.exit(0) stops the java virtual
machine. 0 means normal termination.
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How about the panel object
What are the panel objects responsibilities? ge
t input? _____ repaint itself?
_____ keep track of the egg count?
_____ hold the data it needs to
repaint itself? _____ Do we want our panel to
inherit properties and methods from any existing
classes? _____
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How about the panel object
What are the panel objects responsibilities? ge
t input? No, thats the TextFields job.
repaint itself? Sure, thats its main job.
keep track of the egg count? Yes,
better here where its
needed
hold the data it needs to repaint itself? Yes Do
we want our panel to inherit properties from any
existing classes? Sure, we want to re-use
existing code whenever possible.
74
How about the panel object
When should the panel object repaint
itself? What will the panel need to repaint
itself? Who actually calls the paintComponent
method?
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How about the panel object
When should the panel object repaint itself?
When a new input arrives from the user.
When the egg count changes. What will the
panel need to repaint itself? A graphics
object to draw on. Who actually calls the
paintComponent method? While we have to
provide a paintComponent method we dont
call it directly. Its called by the Java
run-time environment after we make a call
on repaint.
76
class EggPanel extends JPanel public void
paintComponent(Graphics g)
super.paintComponent(g) Graphics2D g2
(Graphics2D)g // draw eggCount
ellipses with random centers Random
generator new Random() for (int i 0 i
lt eggCount i) double x getWidth()
generator.nextDouble() double y
getHeight() generator.nextDouble()
Ellipse2D.Double egg new Ellipse2D.Double(x, y,
EGG_WIDTH, EGG_HEIGHT)
g2.draw(egg)
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public void setEggCount(int count)
eggCount count repaint()
private int eggCount private static final
double EGG_WIDTH 30 private static final
double EGG_HEIGHT 50
78
Java Threads

• Four kinds of thread programming
• Applications
• A GUI application
• A server application

79
Four kinds of thread programming

• 1) Unrelated threads
• 2) Related but unsynchronized threads
• 3) Mutually-exclusive threads
• 4) Communicating mutually-exclusive
• threads

We will look at only the first two kinds.
80
Unrelated threads
class Coffee extends Thread Coffee(String
name) super(name) public void run()
for(int n 1 n lt 3 n)
System.out.println("I like coffee") yield()
System.out.println(this.getName()) yield()

81
class Tea extends Thread Tea(String name)
super(name) public void run()
for(int n 1 n lt 3 n) System.out.printl
n("I like tea") yield() System.out.println(thi
s.getName()) yield()
82
public class Drinks public static void
main(String args)
System.out.println("I am main")
Coffee t1 new Coffee("Wawa Coffee") Tea
t2 new Tea(Sleepy Time Tea") t1.start()
t2.start()
System.out.println("Main is done")
83
Output
I am main Main is done I like coffee I like
tea Wawa Coffee Sleepy Time Tea I like coffee I
like tea Wawa Coffee Sleepy Time Tea I like
coffee I like tea Wawa Coffee Sleepy Time Tea
Main finishes right away
Threads are sharing time
This program has three threads.
84
Unrelated Threads Part II

• Using sleep() in unrelated threads
• The call sleep(millis) puts the currently
  executing thread to
• sleep for at least the specified number of
  milliseconds. "At
• least means there is no guarantee the thread
  will wake up
• in exactly the specified time. Other thread
  scheduling can
• interfere.

85
class Coffee extends Thread Coffee(String
name) super(name) public void run()
for(int n 1 n lt 3 n)
System.out.println("I like coffee")
try
sleep(1000) // 1 second
catch(InterruptedExce
ption e) System.out.println(this.
getName())
86
class Tea extends Thread
Tea(String name) super(name)
public void run() for(int n 1 n lt 5
n) System.out.println("I like
tea") System.out.println(getName())

87
public class Drinks2 public static void
main(String args)
System.out.println("I am main")
Coffee t1 new Coffee("Wawa Coffee")
Tea t2 new Tea("China Tea")
t1.start() t2.start()
System.out.println("Main is done")
88
I am main Main is done I like coffee I like
tea China Tea I like tea China Tea I like
tea China Tea I like tea China Tea I like
tea China Tea Wawa Coffee I like coffee Wawa
Coffee I like coffee Wawa Coffee
After I like coffee, the coffee thread goes to
sleep and the tea thread gets to finish and die.
1 second pausing after each I like coffee
89
Yield() and Sleep()

• Yield() may have no effect on some
  implementations.
• The thread scheduler might make no effort toward
  fairness.
• The yielding thread may be picked again even
  though other threads want a turn.
• It is a good idea to call sleep() instead.

90
An Example Without Threads
Black ball bounces for awhile and then stops. If
you then click start, a new ball bounces for
awhile and then stops. Close only works between
balls. If the ball is moving and you click close,
the close message is queued.
91
// From Cay Horstmann Core Java 2 Advanced import
java.awt. import java.awt.event. import
javax.swing. public class Bounce public
static void main(String args) JFrame
frame new BounceFrame() frame.show()

92
class BounceFrame extends JFrame public
BounceFrame() setSize(300, 200)
setTitle("Bounce")
addWindowListener(new WindowAdapter()
public void windowClosing(WindowEvent e)
System.exit(0)
)
93
Container contentPane getContentPane()
canvas new JPanel()
contentPane.add(canvas, "Center") JPanel p
new JPanel() addButton(p,
"Start", new ActionListener()
public void actionPerformed(ActionEvent evt)
Ball b new Ball(canvas)
b.bounce() )
94
addButton(p, "Close", new
ActionListener() public void
actionPerformed(ActionEvent evt)
System.exit(0) )
contentPane.add(p, "South") public
void addButton(Container c, String title,
ActionListener a) JButton b new
JButton(title) c.add(b)
b.addActionListener(a) private JPanel
canvas
95
class Ball public Ball(JPanel b) box b
public void draw() Graphics g
box.getGraphics() g.fillOval(x, y, XSIZE,
YSIZE) g.dispose()
96
public void move() Graphics g
box.getGraphics() g.setXORMode(box.getBackg
round()) g.fillOval(x, y, XSIZE, YSIZE)
x dx y dy Dimension d
box.getSize() if (x lt 0) x 0 dx
-dx if (x XSIZE gt d.width)
x d.width - XSIZE dx -dx if (y lt
0) y 0 dy -dy if (y YSIZE
gt d.height) y d.height - YSIZE dy
-dy g.fillOval(x, y, XSIZE, YSIZE)
g.dispose()
97
public void bounce() draw() for
(int i 1 i lt 1000 i) move()
try Thread.sleep(5)
catch(InterruptedException e)
private JPanel box private static final int
XSIZE 10 private static final int YSIZE
10 private int x 0 private int y 0
private int dx 2 private int dy 2
98
Bouncing With Threads
The close button works in an instant. Each time
the start button is clicked a new ball appears.
The screen above shows four fast moving bouncing
balls.
99
We use start() rather than bounce() on the ball
object
addButton(p, "Start", new
ActionListener() public void
actionPerformed(ActionEvent evt)
Ball b new Ball(canvas)
b.start() )
100
and have the Ball class extend Thread and
implement run() rather than bounce().
class Ball extends Thread public void run()
try draw() for (int i 1
i lt 1000 i) move()
sleep(5)
catch(InterruptedException e)
101
Ping Pong

• Adapted from "The Java Programming Language",
  Arnold
• and Gosling
• After a thread is created, you can configure it
  set its name,
• its initial priority, and so on.
• The start() method spawns a new thread of control
  based on
• the data in the thread object and then returns.
  Now, the
• Java virtual machine invokes the new thread's run
  method,
• making the thread active.
• When a thread's run method returns, the thread
  has exited.
• The thread may be manipulated with a number of
  methods,
• including the interrupt() method as shown in
  this example.

102
public class PingPong extends Thread private
String word private int delay public
PingPong(String whatToSay, int delayTime)
word whatToSay delay delayTime
103
public void run() try for()
System.out.println(word" ")
sleep(delay)
catch (InterruptedException e)
System.out.println("Interrupted!!!!!") return

104
public static void main(String args)
PingPong t1 new PingPong("\tping",3
3) t1.start()
PingPong t2 new PingPong("Pong",100)
t2.start()
try Thread.sleep(5000)

catch(InterruptedException e) // will not be
printed System.out.println("Good morning")
return

105
Thread myThread Thread.currentThread()
for (int t 1 t lt 10 t)
System.out.println("In Main..."
myThread.getName())
t1.interrupt()
106
C\McCarthy\threads\PingPonggtjava PingPong
ping Pong ping ping
ping Pong ping ping
ping Pong ping ping ping

Main is asleep.
For 5 seconds ping and pong take turns
sleeping and running
107
Pong ping ping
ping Pong In Main...main In Main...main In
Main...main In Main...main In Main...main In
Main...main In Main...main In Main...main In
Main...main In Main...main Interrupted!!!!! Pong P
ong Pong Pong Pong
Main wakes up
Main interrupts Ping and ping dies.
Pongs forever or until until ctrl-c
108
A Thread Application --A Simple Web Server

• Responds by sending the same file on each hit
• Creates a new thread on each hit

109
// A simple web server // Responds with the same
file on each hit import java.net. import
java.io. import java.util. public class
OneFile extends Thread static String
theData "" static String contentType
static int contentLength Socket
theConnection
110
// construct each OneFile object with an
existing socket public OneFile(Socket s)
theConnection s // run
the following code on each object public void
run() try // get a
PrintStream attached to this socket
PrintStream os new PrintStream(

theConnection.getOutputStream())
// get a DataInputStream attached to this socket
DataInputStream is new
DataInputStream(
theConnection.getInputStream())
// read a line from the socket
String request is.readLine()

111
// HTTP/1.0 and later send a MIME
header if(request.indexOf("HTTP/")
! -1) // we need to
read the rest of the MIME header
while(true)
String thisLine is.readLine()
if(thisLine.trim().equals("")) break

// respond to the client
os.print("HTTP/1.0 200 OK\r\n")
// send the date
Date now new Date()
os.print("Date " now "\r\n")
// send our name
os.print("Server OneFile 1.0\r\n")

112
// send the
contentLength
os.print("Content-length " contentLength
"\r\n") //
send the content type
os.print("Content-type " contentType
"\r\n\r\n") //
send the file in the string
os.println(theData)
theConnection.close()
catch(IOException e)
113
// main loads the file and creates the object
on every hit public static void main(String
args ) int thePort ServerSocket
ss Socket theConnection
FileInputStream theFile // cache the
file try // open file and create
a DataInputStream theFile new
FileInputStream(args0)
DataInputStream dis new DataInputStream(theFile)

114
// determine the content type of this
file if(args0.endsWith(".html")
args0.endsWith(".htm") )
contentType "text/html"
else contentType "text/plain"
// read the file into the
string theData try
String thisLine
while((thisLine dis.readLine()) ! null)
theData thisLine "\n"

catch(Exception e)
System.err.println("Error " e)

115
catch(Exception e) System.err.println(
e) System.err.println("usage java
onefile filename port")
System.exit(1) // set the port to
listen on try thePort
Integer.parseInt(args1) if(thePort lt
0 thePort gt 65535) thePort 80
catch(Exception e) thePort 80

116
// create a server socket try ss
new ServerSocket(thePort)
System.out.println("Accepting connections on port
"
ss.getLocalPort()) System.out.println("
Data to be sent") System.out.println(t
heData) while(true) //
stop and wait for a connection
Socket socketTemp ss.accept() //
we have a socket so create a handler
OneFile fs new OneFile(socketTemp)
// start the handler running
fs.start()
catch(IOException e) System.out.println("Socket
error")