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CIS3023: Programming Fundamentals for CIS Majors II Summer 2010 Ganesh Viswanathan Introduction to Applets Course Lecture Slides 29 th July 2010
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Applets Applets are small applications accessed on an Internet server, transported over the networks, automatically installed and run as part of a web document. At the client, applets get limited access to resources to be able to produce graphics, multimedia UI, run computations, etc. without risk of viruses or breaching data integrity.
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Applets Applet Code Example: HelloWorld.java import java.awt.Graphics; import java.applet.Applet; public class HelloWorld extends Applet{ public void paint(Graphics g){ g.drawString("Hello World!", 120, 80); } Every applet must be a subclass of Applet.
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Applets Web document: HelloWorld.html Applet example
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Abstract Window Toolkit (AWT) The Abstract Window Toolkit (AWT) is Java's original platform-independent windowing, graphics, and user- interface widget toolkit. Applets interact with the user through the AWT, not through the console-based I/O classes. AWT is a part of Java Foundation Classes (JFC), the standard API for providing a graphical user interface (GUI) for a Java program.
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Abstract Window Toolkit (AWT) AWT contains support for a window-based, graphical interface. AWT supports graphics through components (visible UI elements-buttons/ labels/ textfields) and containers (components that contain and organize other components). All containers inherit from the java.awt.Container base class, which itself inherits from java.awt.Component
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Applets Do not have main() method Instead applet begins execution when the name of its class is passed to an applet viewer or to a network browser. Compile the applet in the same way as a normal java application) In the example, the paint() method defined by AWT and overridden by the applet helps to redraw output on screen.
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Applets Applets are event-driven. User initiates interaction with an applet. These interactions are sent to the applet as “events” to which the applet must respond. Example: When the user clicks on a button in the applet window, a button-click event is generated.
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Applets In your applet override a set of methods that help the browser or applet-viewer to interface to the applet and control its execution. Applet class defines – init(), start(), stop(), destroy() AWT Component class defines paint() method.
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Applet Skeleton import java.awt.*; import java.applet.*; public class MyAppletSkeleton extends Applet { // browser calls init when applet is first loaded public void init( ){ /* initialization */ } // called second, after init. Also called whenever applet is restarted public void start( ){ /* start or resume execution */ } //called when the applet is stopped public void stop( ){ /* suspends execution */ } //called when applet is terminated. Last method executed public void destroy( ){ /* perform shutdown operations */ } //called when an applet’s window must be restored (redrawn) public void paint(Graphics g){ /* redisplay contents of window */ } }
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Applet Skeleton import java.awt.*; import java.applet.*; public class MyAppletSkeleton extends Applet { // browser calls init when applet is first loaded public void init( ){ /* initialization */ } // called second, after init. Also called whenever applet is restarted. public void start( ){ /* start or resume execution */ } //called when the applet is stopped. public void stop( ){ /* suspends execution */ } //called when applet is terminated. Last method executed. public void destroy( ){ /* perform shutdown operations */ } //called when an applet’s window must be restored (redrawn) public void paint(Graphics g){ /* redisplay contents of window */ } }
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Applets Further examples.
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Get more info! Java docs: java.applet http://download-llnw.oracle.com/javase/1.5.0/docs/api/java/applet/package- summary.htmlhttp://download-llnw.oracle.com/javase/1.5.0/docs/api/java/applet/package- summary.html Java docs: java.awt http://java.sun.com/j2se/1.5.0/docs/api/java/awt/package-summary.html http://java.sun.com/j2se/1.5.0/docs/api/java/awt/package-summary.html http://java.sun.com/products/jdk/awt/#what JFC http://docstore.mik.ua/orelly/java-ent/jfc/ch02_04.htm#jfcnut-ch-2-tab-awtcont
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