1. APPLETS CSC 171 FALL 2004 LECTURE 6

2. APPLETS Graphical Java programs Run inside web browser Platform-neutral Easy deployment--loads when needed Secure

3. Applets Applets are Java prgrams that can be embedded in Hypertext Markup Language (HTML) documents The browser that executes an applet is generically knows as the applet container So, often we use appletviewer

4. How Applets Work

5. HTML Text and tags: Java is an object-oriented programming language Browser renders the tags: Java is an object-oriented programming language Bulleted list (like this one) is defined by tags......... Use <> for <> symbols

6. Simple HTML Ted Pawlicki's CSC 171 HTML Hello Ted!

7. Applet Methods Applets have no “main()” Rather, it has key methods that deal with the unique situation of applets

8. Key Applet Methods init start paint stop destroy

9. Key Applet Methods public void init() public void start() public void paint(Graphics g) public void stop() public void destroy()

10. public void init() Called once by appletviewer or browser Called when an applet is loaded Performs initialization – Instance variables – GUI components – Loading sounds & images (multimedia) – Creation of threads (animation)

11. public void start() Called after the init method completes Called every time the user of the browser returns to the HTML page Performs tasks that must be repeated when the applet is revisited – Restarting an animation

12. public void paint(Graphics g) Called after init() method completes and start() has started “Draws stuff” on the applet The system hands the applet a Graphics object to draw stuff on Automatically recalled whenever the applet needs to be repainted – uncovering a covered window

13. public void stop() Called when the applet should stop executing – When the user leaves the HTML page Perform tasks necessary to suspend applet – “pausing” animations

14. public void destroy() Called when the applet is removed from memory Performs tasks to de-allocate resources

15. repaint() Paint is normally called by the applet container We sometimes change the applet’s appearance based on user input We might like to call paint() directly However, in order to call paint, we have to pass it a Graphics object But the container owns the Graphics object repaint() invokes update() which invokes paint with the appropriate graphics object

16. Some HTML Ted Pawlicki's CSC 171 First Applet

17. Some Java import java.awt.*; import java.applet.Applet; public class FirstApplet extends Applet { public void paint(Graphics g) { g.drawString(“Hello Ted!", 20, 40); }

18. Cooler Graphics class MyApplet extends Applet { public void paint(Graphics g){ Graphics2D g2 = (Graphics2D)g; // add drawing operations... } }

19. Graphical Shapes Shape classes Ellipse2D.Double, Line2D.Double, etc. import java.awt.geom.Ellipse2D; // no.Double Must construct and draw the shape Ellipse2D.Double easterEgg = new Ellipse2D.Double(5, 10, 15, 20); g2.draw(easterEgg)

20. Ellipse

21. Lines Line2D.Double segment = new Line2D.Double(x1, x2, y1, y2); More object-oriented to use Point2D.Double for the end points: Point2D.Double from = new Point2D.Double(x1, y1); Point2D.Double to = new Point2D.Double(x2, y2); Line2D.Double segment = new Line2D.Double(from, to); Draw thick lines: g2.setStroke(new BasicStroke(4.0F)); // 4 pixels

22. Colors Specify red, green, blue between 0.0F and 1.0F Color magenta = new Color(1.0F, 0.0F, 1.0F) Standard colors Color.black Color.yellow Color.pink... Set color in graphics context: g2.setColor(Color.pink); Then draw or fill shapes g2.fill(easterEgg);

23. FONTS Specify text and base point: g2.drawString("Applet", 50, 100); Font object has – face name (Serif, SansSerif, Monospaced,...) – style (Font.PLAIN, Font.BOLD, Font.ITALIC ) – point size (12 point = normal size) g2.setFont(new Font("Serif", Font.BOLD, 36));

24. Baseline

25. “Local” or “Relative” Coordinate System

26. The whole object has a location public Car(double x, double y){ xLeft = x; yTop = y; }

27. The object is drawn “relative” to the whole object’s location public void draw(Graphics2D g2) { Rectangle2D.Double body = new Rectangle2D.Double(xLeft, yTop+10, 60, 10); … Ellipse2D.Double rearTire = new Ellipse2D.Double(xLeft + 40, yTop + 20, 10, 10); …..