Java Threads Part II

1
Java ThreadsPart II
2
Lecture Objectives

• To understand the concepts of multithreading in
  Java
• To be able to develop simple multithreaded
  applications in Java

3
The Runnable Interface

• Another way to create a thread is to have a class
  implement the Runnable interface
• The Runnable interface has one method heading
• public void run()
• A class that implements Runnable must still be
  run from an instance of Thread
• This is usually done by passing the Runnable
  object as an argument to the thread constructor

4
The Runnable Interface An Outline

• public class ClassToRun extends SomeClass
  implements Runnable
• . . .
• public void run()
• // Fill this as if ClassToRun
• // were derived from Thread
• . . .
• public void startThread()
• Thread theThread new Thread(this)
• theThread.run()
• . . .

5
The Runnable Interface An Example
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The Runnable Interface An Example (Contd)
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The Runnable Interface An Example (Contd)
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The Runnable Interface An Example (Contd)
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The Runnable Interface An Example (Contd)
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Example 1

• import javax.swing.
• public class TimeThread extends JFrame implements
  Runnable
• private JTextField sec, min, hrs
• private JPanel panel
• private int time 0
• public TimeThread()
• super(Time")
• sec new JTextField(3) sec.setEditable(fals
  e) //makes textfield uneditable
• min new JTextField(3) min.setEditable(fals
  e)
• hrs new JTextField(3) hrs.setEditable(fals
  e)
• panel new JPanel()
• panel.add(hrs) panel.add(min)
  panel.add(sec)

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Example 1- Continued

• public void run()
• try
• while(true)
• Thread.sleep(1000) time
• sec.setText(time60 "") //Display
  seconds
• min.setText((time (time/3600)3600)/60
  "") //Display minutes
• hrs.setText(time/3600 "") //Display
  hours
• catch(InterruptedException e)
• public static void main(String args)
• TimeThread t new TimeThread()
• Thread mytime new Thread(t)
• mytime.start()

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Threads For Animation

• Threads can also be used to create animations.
• In the next example we show a program where a
  thread is used to create an animation of a ball
  moving vertically.
• The run() method increments the y coordinate of
  the ball to be drawn. If the y-coordinate exceeds
  the height of the window, the ball is reflected
  back by negating the increment.
• The complete program appears in the next slide.

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Example 2 Thread Animations
import java.awt. import javax.swing. public
class UpDown extends JFrame public UpDown
() setSize(400,500) add(new
DrawingArea()) class DrawingArea
extends JPanel implements Runnable int
radius, xc, yc Thread t public
DrawingArea() radius 20 xc 30
//signifies x location yc 20 //signifies
y location Thread t new Thread (this)
t.start()
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Example 2 continued
public void paintComponent(Graphics g)
super.paintComponent(g)
g.setColor(Color.blue) g.fillOval(xc -
radius, yc - radius, 2radius, 2radius)
public void run() int
incry10 int sleepFor 50
while(true) yc incry
repaint() if(yc - radius lt 0 yc
radius gt getSize().height)
incry -incry //reflect the ball back
try Thread.sleep (sleepFor)
catch(InterruptedException e)
// end while public static void
main(String args) new UpDown().setVisible(t
rue)
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Example 3 Salaam Shabab Animation

• import java.awt.
• import java.awt.event.
• import javax.swing.
• class AnimationPanel extends JPanel implements
  Runnable
• private Font myFont
• private int increment 1
• public int xSize, ySize, yCoord 0
• int delay
• Thread animator
• private boolean onOfftrue
• public AnimationPanel(int delay)
• xSize400
• ySize350
• setSize(xSize, ySize)
• myFont new Font ("Serif",
  Font.ITALIC, 30)
• animator new Thread(this)
• animator.start()
• public void setOnOff(boolean onOff)

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Example 3 Shabab Animation (contd)

• public void paintComponent(Graphics g)
• super.paintComponent(g)
• g.setColor(Color.yellow)
• g.fillRect(0,0,xSize, ySize)
• g.setColor (Color.red)
• g.setFont(myFont)
• if(onOff)
• g.drawString ("Salaam ",
  xSize/2-100, ySize/2 yCoord)
• g.drawString ("Shabab!", xSize/2,
  ySize/2 - yCoord)
• public void run ()
• while(true)
• yCoord yCoord increment//yCoord
  min is -150 and max 150
• if((yCoord (ySize-50)/2 (yCoord
  -(ySize-50)/2)))
• increment -increment //
  increment by -1 now
• try
• Thread.sleep(delay)
• catch(InterruptedException e)

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Example 3 Shabab Animation (contd)

• public class SalamShababAnimation extends
  JApplet
• private Button myButton
• private boolean onOffButton true
• private AnimationPanel ap
• public void init() //validate parsing the
  parameter "fps"
• int delay Integer.parseInt(getParamete
  r("fps"))
• delay (delaylt10)? 10 delay
• Container cp getContentPane()
• cp.setLayout(new BorderLayout())
• ap new AnimationPanel(delay)
• myButton new Button ("Start/Stop")
• myButton.addActionListener(new
  ActionListener()
• public void actionPerformed(ActionE
  vent ae)
• onOffButton !onOffButton
• ap.setOnOff(onOffButton)
• )
• cp.add(myButton,BorderLayout.NORTH)
• cp.add(ap, BorderLayout.CENTER)

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Example 4 Car Race Animation

• import java.awt.
• import java.awt.event.
• import javax.swing.
• import java.util.
• class DrivingPanel extends JPanel implements
  Runnable
• private int delay
• private Thread animator
• private Image car
• static final int WIDTH 600
• static final int HEIGHT 200
• private int xPosition, speed
• private Random random
• public DrivingPanel(Image car, int delay)
• this.car car
• this.delay delay
• setSize(WIDTH,HEIGHT)
• xPosition getWidth()
• random new Random()
• speed random.nextInt(5)//1

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Example 4 Car Race Animation (contd)

• public void run()
• while (true)
• repaint()
• speed random.nextInt(5)1
• xPosition - speed
• if (xPosition lt -car.getWidth(this))
• xPosition getWidth()
• try
• Thread.sleep(delay)
• catch (InterruptedException e)
• break
• public void paintComponent(Graphics g)
• super.paintComponent(g)
• g.setColor(Color.white)
• g.fillRect(0, 0, getWidth(),
  getHeight())
• g.drawImage(car, xPosition,
  getHeight()/2, this)

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Example 4 Car Race Animation (contd)

• public class CarRaceAnimation extends JApplet
• public void init() // You should validate
  parsing the parameter!
• int delay Integer.parseInt(getParameter("f
  ps"))
• delay (delaylt10)? 10 delay
• Image car getImage(getCodeBase(),"car.gif"
  )
• DrivingPanel lane1 new DrivingPanel(car,
  delay)
• DrivingPanel lane2 new DrivingPanel(car,
  delay)
• Container cp getContentPane()
• cp.setLayout(new GridLayout(2,1))
• cp.add(lane1)
• cp.add(lane2)

• Download the car image used in the example
  from here.
• You can also obtain the rocket image for the
  next example.

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Example 5 Rocket Launcher

• import java.applet.
• import java.awt.
• import java.awt.event.
• import javax.swing.
• public class RocketLauncher extends JApplet
  implements Runnable, ActionListener
• private Image rocket
• private int x, y, sec10
• private Thread myThread
• private Timer timer new Timer(1000,this)
• JTextField tf new JTextField(5)
• JButton b new JButton("Start Count Down")
• public void init()
• rocket Toolkit.getDefaultToolkit().getImag
  e("rocket.jpg")
• x 50
• y getSize().height-rocket.getHeight(this)-
  380
• myThread new Thread(this)
• tf.setText(" "sec" ")
• b.addActionListener(this)

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Example 5 Rocket Launcher (contd)

• public void actionPerformed( ActionEvent ae)
• if(ae.getSource() b)
• timer.start()
• if(ae.getSource() timer)
• if(--secgt0)
• tf.setText(" "sec" ")
• else
• timer.stop()
• myThread.start()
• public void run()
• while (y-- ! -rocket.getHeight(this))
• try
• myThread.sleep(10)
• catch (InterruptedException e)
• repaint()

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Example 5 Rocket Launcher (contd)

• public void paint(Graphics g)
• g.drawImage(rocket,x,y,null)
• public static void main(String args)
• JFrame frame new JFrame("My Rocket
  Launch Pad")
• frame.setSize(400,750)
• Container cp frame.getContentPane()
• cp.setLayout(new GridLayout(1,2))
• JPanel p new JPanel()
• JPanel p1 new JPanel()
• p.setLayout(new BoxLayout(p,BoxLayout.Y_AXIS
  ))
• RocketLauncher applet new
  RocketLauncher()
• p.add(applet.b)
• p1.add(applet.tf)
• p.add(p1)
• cp.add(p)
• applet.setBackground(Color.white)
• cp.add(applet)
• frame.setVisible(true)