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Applet and Graphics

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  1. Applet and Graphics

  2. Inheritance Hierarchy of GUI Classes

  3. Constructors and Methods of the class Component

  4. Constructors and Methods of the class Component

  5. Constructors and Methods of the class Component

  6. Constructors and Methods of the class Container

  7. Applets • Applet: a Java program that is embedded within a Web page and executed by a Web browser • Create an applet by extending the class JApplet • class JApplet contained in package javax.swing

  8. Members of class JApplet

  9. Members of class JApplet

  10. Applets • No main method • Methods init, start, and paint guaranteed to be invoked in sequence • To develop an applet • Override any/all of the methods above

  11. Applet Methods • init Method • Initializes variables • Gets data from user • Places various GUI components • paint Method • Performs output

  12. Skeleton of a Java Applet import java.awt.Graphics; import javax.swing.JApplet; public classWelcomeApplet extends JApplet { }

  13. Applet Displaying Welcome Message //Welcome Applet import java.awt.Graphics; import javax.swing.JApplet; public class WelcomeApplet extends JApplet { public void paint(Graphics g) { super.paint(g); //Line 1 g.drawString(“Welcome to Java Programming”, 30, 30); //Lineƒ2 } }

  14. HTML to Run Applet

  15. class Font • Shows text in different fonts • Contained in package java.awt • Available fonts • Serif/SanSerif • Monospaced • Dialog/DialogInput • Arguments for constructor • String specifying the Font face name • int value specifying Font style • int value specifying Font size • Expressed in points (72 points = 1 inch)

  16. Constructors and Methods of the class Font

  17. class Color • Shows text in different colors • Changes background color of component • Contained in package java.awt

  18. Constructors of the class Color

  19. Methods of the class Color

  20. Methods of the class Color

  21. Constants Defined in the class Color

  22. class Graphics • Provides methods for drawing items such as lines, ovals, and rectangles on the screen • Contains methods to set the properties of graphic elements including clipping area, fonts, and colors • Contained in the package java.awt

  23. Constructors and Methods of the class Graphics

  24. Constructors and Methods for the class Graphics

  25. Constructors and Methods for the class Graphics

  26. Constructors and Methods for the class Graphics

  27. Applets Derived from JApplet No main method Uses init method Displayed by HTML Sets title in HTML Size set in HTML Applet closes when HTML doc closes GUI applications class extends JFrame Invokes main method Uses constructors Uses method setVisible Uses setTitle method Uses method setSize Closes with Exit button Differences Between Applets and GUI Applications

  28. Converting a GUI Application to an Applet • Change JFrame to JApplet • Change constructor to method init • Remove method calls such as setVisible, setTitle, setSize • Remove the method main • If applicable, remove Exit button/all code associated with it (e.g. action listener)