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JavaBoutique : Articles :

An Illustration of these Techniques

Contents
Introduction
Intro pt 1
Intro pt 2
Intro pt 3
Intro pt 4
An Illustration of these Techniques
An Applet Example
An Active X Example
A Pseudo-Constructor Example
Pseudo-Constructor pt 2
Applet Persists Indefinitely; Breaks into JavaScript
Persistence
Conclusion

2. An Active X Example

The Java code below is interpreted by Microsoft Visual J++ Version 6, and used to form an Active X object which will be loaded by the following two HTML pages. The first, or something similar to it, is generated automatically by the said Visual J++ compiler and saved as HTML Page1.htm. Notice that we have inserted, into the said automatically generated code, a hyperlink to a Page2.htm.

<HTML>
<HEAD>
<TITLE></TITLE>
</HEAD>
<BODY>
<OBJECT
  classid="java:com.ms.wfc.html.DhModule"
  height=0 width=0 ... VIEWASTEXT
  id=OBJECT1>
<PARAM NAME=__CODECLASS VALUE=Class1>
<PARAM NAME=CABBASE VALUE=Project3.CAB>
</OBJECT>
<A HREF="Page2.htm">Page2.htm</A>
</BODY>
</HTML>

Page2.htm is produced by copying the contents of Page1.htm into an empty HTML page, naming this said page Page2.htm, and altering the hyperlink to Page2.htm, in the said copied code from Page 1.htm, into a return link to Page1.htm:

<HTML>
<HEAD>
<TITLE></TITLE>
</HEAD>
<BODY>
<OBJECT
  classid="java:com.ms.wfc.html.DhModule"
  height=0 width=0 ... VIEWASTEXT
  id=OBJECT1>
<PARAM NAME=__CODECLASS VALUE=Class1>
<PARAM NAME=CABBASE VALUE=Project3.CAB>
</OBJECT>
<A HREF="Page1.htm">Page1.htm</A>
</BODY>
</HTML>

The code:

import com.ms.wfc.html.*;
import com.ms.wfc.ui.*;

public class Class1 extends DhDocument{
  public Class1() {
    if(Constants.form == null){
      Constants.form = new Form();
      Constants.form.setBounds((int)Constants.formx.intValue(),
        (int)(Constants.formy.intValue()),300,300);
      Constants.form.setVisible(true);
      }
    Constants.form.bringToFront();
  }

  public void dispose() {
    Constants.formx = new Integer(Constants.form.getBounds().x);
    Constants.formy = new Integer(Constants.form.getBounds().y);
    Constants.form.dispose();
    Constants.form = null;
    super.dispose();
    }
  }

  abstract class Constants{
    static Form form;
    static Integer formx = new Integer(225);
    static Integer formy = new Integer(150);
  }

In contrast to the applet example, which uses the Abstract Windows Toolkit, there appears to be no stability problem at all in the Active X implementation of persistence, which uses Windows Foundation Classes. This demonstrates graphically that persistence can be used to generate very dependable code.

The previous two examples can be tested in the following manner.
- 1) Place all relevant files into the same directory.
- 2) Load Page 1 into a browser.
- 3) Use the mouse to move the frame (or in the case of Active X, the form) to a different location.
- 4) Use the browser to jump to Page 2. Notice that the frame does not come up in the original location but rather retains its new position.
- 5) Use the browser to jump to an unrelated page and then reload either Page 1 or Page 2. You will notice that the frame returns and maintains its latest position.
- 6) Repeat steps 3) to 5) as often as you wish.

Next ->


Lane Friesen

lanelise@dowco.com

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