Java Threads Part II

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

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

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(); }... }

The Runnable Interface: An Example

The Runnable Interface: An Example (Cont’d)

1.import javax.swing.*; 2.public class TimeThread extends JFrame implements Runnable { private JTextField sec, min, hrs; 5. private JPanel panel; 6. private int time = 0; public TimeThread() { 9. super(“Time"); sec = new JTextField(3); sec.setEditable(false); //makes textfield uneditable 12. min = new JTextField(3); min.setEditable(false); 13. hrs = new JTextField(3); hrs.setEditable(false); panel = new JPanel(); panel.add(hrs); panel.add(min); panel.add(sec); getContentPane().add(panel); pack(); setVisible(true); 20. } Example 1

1. public void run() 2. { 3. try { 4. while(true) { 5. Thread.sleep(1000); time++; 6. sec.setText(time%60 + ""); //Display seconds 7. min.setText((time – (time/3600)*3600)/60 + ""); //Display minutes 8. hrs.setText(time/ ""); //Display hours 9. } 10. } catch(InterruptedException e) {} 11. } 12. public static void main(String[] args) 13. { 14. TimeThread t = new TimeThread(); 15. Thread mytime = new Thread(t); 16. mytime.start(); 17. } 18.} Example 1- Continued

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.

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(); }

public void paintComponent(Graphics g) { super.paintComponent(g); g.setColor(Color.blue); g.fillOval(xc - radius, yc - radius, 2*radius, 2*radius); } public void run(){ int incry=10; int sleepFor = 50; while(true) { yc += incry ; repaint(); if(yc - radius 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(true); }} Example 2 – continued

Example 3: ‘Salaam Shabab’ Animation 1.import java.awt.*; 2.import java.awt.event.*; 3.import javax.swing.*; 4.class AnimationPanel extends JPanel implements Runnable { 5. private Font myFont; 6. private int increment = 1; 7. public int xSize, ySize, yCoord = 0; 8. int delay; 9. Thread animator; 10. private boolean onOff=true; 11. public AnimationPanel(int delay) { 12. xSize=400; 13. ySize=350; 14. setSize(xSize, ySize); 15. myFont = new Font ("Serif", Font.ITALIC, 30); 16. animator = new Thread(this); 17. animator.start(); 18. } 19. public void setOnOff(boolean onOff) { 20. this.onOff = onOff; 21. }

Example 3: ‘Shabab’ Animation (cont’d) 22. public void paintComponent(Graphics g) { 23. super.paintComponent(g); 24. g.setColor(Color.yellow); 25. g.fillRect(0,0,xSize, ySize); 26. g.setColor (Color.red); 27. g.setFont(myFont); 28. if(onOff) { 29. g.drawString ("Salaam ", xSize/2-100, ySize/2 + yCoord); 30. g.drawString ("Shabab!", xSize/2, ySize/2 - yCoord); 31. } 32. } 33. public void run () { 34. while(true){ 35. yCoord = yCoord + increment;//yCoord min is -150 and max if((yCoord == (ySize-50)/2 || (yCoord == -(ySize-50)/2))) 37. increment = -increment; // increment by -1 now 38. try{ 39. Thread.sleep(delay); 40. } catch(InterruptedException e){} 41. repaint(); 42. } 43. } 44. }

Example 3: ‘Shabab’ Animation (cont’d) 45. public class SalamShababAnimation extends JApplet{ 46. private Button myButton; 47. private boolean onOffButton = true; 48. private AnimationPanel ap; 49. public void init() { //validate parsing the parameter "fps" 50. int delay = Integer.parseInt(getParameter("fps")); 51. delay = (delay<10)? 10 : delay; 52. Container cp = getContentPane(); 53. cp.setLayout(new BorderLayout()); 54. ap = new AnimationPanel(delay); 55. myButton = new Button ("Start/Stop"); 56. myButton.addActionListener(new ActionListener(){ 57. public void actionPerformed(ActionEvent ae){ 58. onOffButton = !onOffButton; 59. ap.setOnOff(onOffButton); 60. }}); 61. cp.add(myButton,BorderLayout.NORTH); 62. cp.add(ap, BorderLayout.CENTER); 63. } 64.}

Example 4: Car Race Animation 1.import java.awt.*; 2.import java.awt.event.*; 3.import javax.swing.*; 4.import java.util.*; 5. class DrivingPanel extends JPanel implements Runnable { 6. private int delay; 7. private Thread animator; 8. private Image car; 9. static final int WIDTH = 600; 10. static final int HEIGHT = 200; 11. private int xPosition, speed; 12. private Random random; 13. public DrivingPanel(Image car, int delay) { 14. this.car = car; 15. this.delay = delay; 16. setSize(WIDTH,HEIGHT); 17. xPosition = getWidth(); 18. random = new Random(); 19. speed = random.nextInt(5);//+1; 20. animator = new Thread(this); 21. animator.start(); 22. }

Example 4: Car Race Animation (cont’d) 23. public void run() { 24. while (true) { 25. repaint(); 26. speed = random.nextInt(5)+1; 27. xPosition -= speed; 28. if (xPosition < -car.getWidth(this)) 29. xPosition = getWidth(); 30. try { 31. Thread.sleep(delay); 32. } catch (InterruptedException e) { 33. break; 34. } 35. } 36. } 37. public void paintComponent(Graphics g) { 38. super.paintComponent(g); 39. g.setColor(Color.white); 40. g.fillRect(0, 0, getWidth(), getHeight()); 41. g.drawImage(car, xPosition, getHeight()/2, this); 42. } 43.}

Example 4: Car Race Animation (cont’d) 44.public class CarRaceAnimation extends JApplet { 45. public void init() { // You should validate parsing the parameter! 46. int delay = Integer.parseInt(getParameter("fps")); 47. delay = (delay<10)? 10: delay; 48. Image car = getImage(getCodeBase(),"car.gif"); 49. DrivingPanel lane1 = new DrivingPanel(car, delay); 50. DrivingPanel lane2 = new DrivingPanel(car, delay); 51. Container cp = getContentPane(); 52. cp.setLayout(new GridLayout(2,1)); 53. cp.add(lane1); 54. cp.add(lane2); 55. } 56.} Download the car image used in the example from here. here You can also obtain the rocket image for the next example.rocket image

Example 5: Rocket Launcher 1.import java.applet.*; 2.import java.awt.*; 3.import java.awt.event.*; 4.import javax.swing.*; 5.public class RocketLauncher extends JApplet implements Runnable, ActionListener { 6. private Image rocket; 7. private int x, y, sec=10; 8. private Thread myThread; 9. private Timer timer = new Timer(1000,this); 10. JTextField tf = new JTextField(5); 11. JButton b = new JButton("Start Count Down"); 12. public void init() { 13. rocket = Toolkit.getDefaultToolkit().getImage("rocket.jpg"); 14. x = 50; 15. y = getSize().height-rocket.getHeight(this)-380; 16. myThread = new Thread(this); 17. tf.setText(" "+sec+" "); 18. b.addActionListener(this); 19. }

Example 5: Rocket Launcher (cont’d) 20. public void actionPerformed( ActionEvent ae) { 21. if(ae.getSource() == b) 22. timer.start(); 23. if(ae.getSource() == timer) 24. if(--sec>0) 25. tf.setText(" "+sec+" "); 26. else{ 27. timer.stop(); 28. myThread.start(); 29. } 30. } 31. public void run() { 32. while (y-- != -rocket.getHeight(this)) { 33. try { 34. myThread.sleep(10); 35. } catch (InterruptedException e) {} 36. repaint(); 37. } 38. } 39. public void update(Graphics g){ 40. paint(g); 41. }

Example 5: Rocket Launcher (cont’d) 42. public void paint(Graphics g) { 43. g.drawImage(rocket,x,y,null); 44. } 45. public static void main(String [] args){ 46. JFrame frame = new JFrame("My Rocket Launch Pad"); 47. frame.setSize(400,750); 48. Container cp = frame.getContentPane(); 49. cp.setLayout(new GridLayout(1,2)); 50. JPanel p = new JPanel(); 51. JPanel p1 = new JPanel(); 52. p.setLayout(new BoxLayout(p,BoxLayout.Y_AXIS)); 53. RocketLauncher applet = new RocketLauncher(); 54. p.add(applet.b); 55. p1.add(applet.tf); 56. p.add(p1); 57. cp.add(p); 58. applet.setBackground(Color.white); 59. cp.add(applet); 60. frame.setVisible(true); 61. applet.init(); 62. } 63.}