Applets (Day 7 of, Java in 21 Days)
  21 Days:   Wk1 . Wk1Ref . Applts . Swing . Grph . D13-14 . D15-21 . D22-28
  cc12:   Miscl . SQL . EJB . Vocab . (NotesHelp) . J2EE . Web
  misl:   21 Days(src) . Dictionary(foldoc) . Unicode . Tables . Print . html
  misl:   F.Allimant . Swing (J.H.University) 



-----Jul/25/2002 THU-FRI   pg.163, "Day   7", Writing Java Applets.
 - Java introduced interative web pages, and is still effective. Macromedia Flash and
   Microsoft ActiveX can do similar things. (pg.163)




   How Applets and Applications Are Different.



-----Jul/25/2002 THU-FRI:  
 - Applications run with a Java interpreter, Applets run on a browser that 
   supports Java.
 - Applet testing may be done with the appletviewer tool in the SDK.
 - "For an applet to run, it must be included on a Web page using HTML tags in 
   the same way images and other elements are included.  When a user..." loads a
   Web page containing an applet, the browser downloads the applet from a web 
   server before it runs. The interpreter is built into the browser.
 - Appropriate limitations, of Applets, on most browsers...
    1. CAN'T read or write files on user's system.
    2. CAN'T communicate w/ internet site other than site serving page of applet.
    3. CAN'T run programs on user's system.
    4. CAN'T load programs stored on user's system, like exe's or dll's.
 - "Appletviewer" does allow limited file access.
 - CAUTION: Get acquainted with known "hostile applets". (It is recomended to web search 
   this topic.) (pg.165.nearBottom)




   Applet Security Restrictions.



-----Aug/13/2002 TUE:  
 - "Java's current version includes a way for a Web user to trust an applet, so that 
   applet can run without restriction on the user's system, just as an application can."
   Specific SECURITY (day.16) controls are available. (pg.166.bottom-167.top)
===Choosing a Java Version (pg.165.bottom)
 1) Java 1.0 will run on all Java-capable browsers.
 2) Java 1.1 for Netscape 4, Internet Explorer 4, Opera 3.6... (and higher).
 3) Java 2 may be used if the Sun add-on called the "Java Plug-in" is installed.
 - Latest version of java is always supported on latest "Appletviewer" in the matching SDK.
 - Prior version's of java are fully documented at java.sun.com/infodocs.
 - (pg.185.paragrph4): Built into most browsers now, is a Java 1.1 interpreter.
    - Version 1.1 offers: an improved user interface, and better handling of events, and more.




   Creating Applets.



-----Aug/13-24/2002 TUE-SAT:  (pggg.167)
===CREATING APPLETS
 - Java applications generally have a main() method. It creates objects, sets instance variables,
   and calls other methods.
 - Java applets do not have a main() method. They have several methods called at
   different points of the applet's execution.
 - All applets are subclasses of either the JApplet or the Applet class. JApplet supports swing.
 - Sample:
   public class myApplet extends javax.swing.JApplet {
           // applet code here
   }
 - Your primary applet class must be declared public, since JApplet is a public class.
 - The browser "calls methods of the JApplet class when specific events take place". 
   (see:pg.167.bottom)
===Major Applet Activities (Aug/19/2002 MON)  (pg.168)
 1) Initialization - public void init() { /*code*/ }  (pg.168)
    - sample /*code*/: setBackground(orange);  // wont be shown until applet window is redrawn.
 2) Starting       - public void start() {   /*code*/ } // start (?) or return to pg.  (pg.169)
 3) Stopping       - public void stop() {    /*code*/ } // when leave pg, or call to stop().  (pg.169)
 4) Destruction    - public void destroy() { /*code*/ } // often not overridden.  (pg.170)
     - kill running threads, or release running objects.
 5) Painting       - public void paint(Graphics g) { /*code*/ } // display to screen  (pg.170)
     - text, line, background, image, etc.
     - paint may run hundreds of times: when initialized, or browser brought from behind other window, different position...
     - "Graphics g" is an instance of class Graphics.  It is created and supplied by the browser.
     - Needed: import of java.awt.Graphics, usually by import statment at top of your Java source.
     - Note: "*" used in w/import statement, does not include subclasses of the package.
     - if you need to force a call to paint, call repaint();
     - if Graphics2D needed cast the "Graphics g" parameter.
     - most applet work is done inside paint();




   Including an Applet on a Web Page, the "APPLET" tag.



-----Aug/24/2002-Sep/04: "APPLET" TAG ANNND ITS ATTRIBUTES  (pg.172-179)
===An Example Applet
 - Watch.html loads Watch.class applet compiled from Watch.java.
    - "APPLET" is just for applets. "OBJECT" can be used instead, and supports more.
    - Each of following are required: <applet code="Watch.class" height="50" width="445">
    - Other attributes besides CODE, WIDTH, and HEIGHT are similar to IMG attributes. 
       . ALIGN=LEFT, RIGHT, TEXTTOP, TOP, ABSMIDDLE, MIDDLE, BASELINE, ABSBOTTOM.
          - To end ALIGN, BR with CLEAR=LEFT, RIGHT, ALL.
       . HSPACE and VSPACE to set pixels between applet and text.
    - CODEBASE is optional and points to a different dir to find class files.




   Java Archives for Faster Download.



-----Sep/04/2002 WED: JAVA ARCHIVES  (pggg.180)
 - "Jar" files can be used to speed loading of an applet when multiple files are involved.
   Without it, each file would need a separate conection.
 - Example of creating a jar file from command line...:
   jar cf Animate.jar *.class *.gif
 - Attribute to name this jar file is ARCHIVE="Animate.jar"





   Applet Parameters.



-----Oct/17/2002 THU:  (pg.181-185)
 - Applications can get parameters from the command line into main().
 - Applets can get parameters from the HTML file containing the applet.
 - Two things needed for applet parameters:
    1) "A special parameter tag in the HTML file."
    2) "Code in your applet to parse those parameters."
 - Example:
      <APPLET CODE="Watch.class" WIDTH="445" HEIGHT="50">
      <PARAM NAME=font VALUE="TimesRoman">
      <PARAM NAME=size VALUE="24">
      Java Applet appears here.
      </APPLET>
 - In the init() method, getParameter() can be called.
    . public String getParameter(String parameterName)
      Returns of getParameter() is the value of the named parameter.
    . parameterName of getParameter() is case sensitive.





   Devloping Java 2 Applets, for Java Plug-in.



-----Oct/23/2002 WED: (page.185)<<
 - The Java Plug-in, is a virtual machine that improves a web browser's Java support.
 - Built into most browsers now, is a Java 1.1 interpreter, developed by the brower developer.
    - Version 1.1 offers: an improved user interface, and better handling of events, and more.
 - Sun offers a Java Plug-In that runs instead of the built in Java interpreter.  For applet
   programmers who want to use the latest java language features.
 - To use the plug-in we need two things:
   1) the browser needs the java plug-in installed, and
   2) the html page must have html code to tell the java plug-in to run the applet.
 - Java Plug-In can be found:
   1) within the SDK 1.3, or
   2) download at http://java.sun.com/products/plugin/
===Using the Plug-In on a Web Page (pg.186):
 - HTML written to tell the java plug-in to run, is considerably more complicated.
 - From the same web page where you can download the plug-in, you also find the HTMLConverter 
   to convert standard html, to html that tells the java plug-in to run the applet.
    - After install, you should add the converter's path to your CLASSPATH (and re-boot).
    - Once installed, run as follows:  java HTMLConverter YourApplet.html
===Running the Plug-In (Oct/30) (pg.187.bottom):
 - If the html specifies that the java plug-in is needed to run, 1) a check is 
   made to see if it is already installed in the browser. 2) If it is not, the
   user will see a pop-up window asking for permision to install the plug-in
   from Sun Microsystems.
 - pg.188: Because the plug-in is so large, Sun recomends to programmers to 
   write applets in java 1.1 or 1.0 for most purposes. And to reserve requiring 
   the plug-in "for intranets, large-scale corporate software, and other 
   projects where the audience is well defined."

===Summary (pg.189):
 - Applets are no longer the focus of Java development, but applets have the most
   end users.
 - The capability to use the graphics user interface, since displayed in
   web pages, gives applet programmers more features with less toil.
 - All applets are subclasses of java.applet.Applet or javax.swing.JApplet class.
[ ]Q: How similar is an applet's init() method to a java aplications main() method?
      99 percent similar?  85 percent?  75 percent?  or less?

// done chapter.





   Vocabulary.



===Virtual Machine - (pg.18): a sort of computer-within-a-computer.
 - Java programs are compiled into machine code (called bytecode) for a virtual machine.
   The virtual machine interprets this bytecode by converting it into a specific 
   processor's machine code.

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B19 - Teach Yourself Java 2 in 21 Days. 2nd ed. Lemay and Cadenhead. © 2001.
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