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Lesson: Intro to Applets

Lesson: Intro to Applets. ICS3M. Learning Objectives. What is an applet? Structure of an Applet 6 standard methods of applet. 2 Kinds of Java Program. Application Has a main method Text based Applet No main method Must inherit from the Applet class. GUI based (using frames).

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Lesson: Intro to Applets

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  1. Lesson: Intro to Applets ICS3M

  2. Learning Objectives • What is an applet? • Structure of an Applet • 6 standard methods of applet

  3. 2 Kinds of Java Program • Application • Has a main method • Text based • Applet • No main method • Must inherit from the Applet class. • GUI based (using frames)

  4. What is an Applet? • An applet is a Java program that can be sent over the Internet and run under web browsers. Show Jag Game Demo

  5. Benefits of Applets • Provide access to GUI features of Java. • They are portable. (i.e. can be run on many different computer platforms)

  6. Structure of an Applet • All applets are classes that inherit from the class Applet. • Each applet must import the Applet class with the statement • import java.applet.Applet;

  7. Defining an Applet import java.applet.Applet; import java.awt.Graphics; public class class-name extendsApplet { // your code } • Every applet must import the Applet and Graphics class. • Every applet must define a subclass of the Applet class.

  8. Applet Methods • Applet class has a number of methods • They are often overridden by new versions of the methods in the new subclass applet.

  9. Methods Overridden

  10. Notes • We will only focused on overloading init, paint, and action methods. • Others will have the default behavior inherited from the Applet class, which in fact do nothing. • Applets can contain other user-defined methods which are called by any of the standard methods.

  11. Applets • Every applet must implement at least one of the following methods: • public void init( ) • public void start ( ) • public void paint (Graphics g) Q: Where can you find the other method signature?

  12. Applet Boilerplate

  13. Running an Applet <html> <head> <title> The ExampleApplet applet </title> </head> <body> <h2> Here is the ExampleApplet applet </h2> <hr> <applet code="ExampleApplet.class" width="300" height="200"> </applet> <hr> </body> </html>

  14. Applets with No Input

  15. Example: HelloWorld • The Graphics object passed into paint method represents the applet’s onscreen drawing context. import java.applet.Applet; import java.awt.Graphics; public class HelloWorld extends Applet { public void paint(Graphics g) { g.drawString(“Hello world!”, 50, 25); } }

  16. Drawing Screen X ( x, y )  ( 0, 0 ) Y

  17. drawString(“Hello World”, 10, 20) ( x, y )  ( 0, 0 ) Hello World Y

  18. Graphic Class • clearRect • drawLine • drawOval • drawRect • drawString • fillRect • setColor • Look up the method signatures for the above methods and use it do complete the House assignment.

  19. Class Exercise • Use methods in Graphics class, write an applet that draws a simple house with a roof and a window as shown below. Your applet must say “My House” at the base of the roof. • Demo “MyHouse” • Demo “Rhyme” • Demo “CircleBlocks” My House

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