...upon choosing this product. Not only will it improve your health, and enhance your general spirituality, it will also clean the bath, cook you breakfast, take care of the children, end armed conflict and invigorate the look of your web page.

You should be careful to check that your unzipping program has named the files correctly. Some DOS programs will name according to the old 8.3 format, rename .class files "*.cla".

If you get lost following these instructions, then there is an online "Dummy's Guide" at http://www.demon.co.uk/davidg/http://www.demon.co.uk/davidg/lakeinst.htm. I shall continue to update this guide to cover any steps that people find problematical.

To include lake in a web page, you should copy all class files into the same directory as the web page and then insert an <APPLET...> tag into the page, e.g.

<applet code="lake" width= height=>
 	<param name="image" value="sunset.jpg"> 
 	<param name="href" value="http://www.demon.co.uk/davidg/spigots.htm"> 
</applet>

Each of the "PARAM" tags passes a value to the applet. The examples shown here are the "image" parameter and the "href" parameter. In general the "PARAM" tag has the following format:

<PARAM name="[PARAMETER NAME]" value="[PARAMETER VALUE]">

Note that in Communicator 4.5 you will need to insert the tags in one at a time. Do this by choosing "Insert/HTML Tag..." from the menu for the <applet...> tag, then each of the <param...> tags and so on. For a full list of the parameters that can be passed to lake, see below.

The following parameters can be passed to the lake:

The IMAGE parameter

JPG or GIF file that you want to reflect.

<applet code=lake width=250 height=250>
<param name=image value="scenic.jpg">
</applet>

The OVERLAY parameter

The JPG or GIF file that you want to appear over the animated image. Quite frequently an overlay would be a GIF file, so that parts of it can be made transparent and allow the lake image to show through.

<applet code=lake width=250 height=250>
<param name=image value="scenic.jpg">
<param name=overlay value="dglogo.gif">
</applet>

The HREF parameter

The URL to link to when the applet is clicked. By default this is http://www.demon.co.uk/davidg.

<applet code=lake width=250 height=250>
<param name=image value="scenic.jpg">
<param name=href value="http://www.javasoft.com">
</applet>

The TARGET parameter

This is the name of the frame you want any linked page to appear in.

<applet code=lake width=250 height=250>
<param name=image value="scenic.jpg">
<param name=href value="http://www.microsoft.com">
<param name=target value="newframe">
</applet>

The UNDERWATER parameter

TRUE if the image is to appear reflected on the underside of the water.

<applet code=lake width=250 height=250>
<param name=image value="scenic.jpg">
<param name=underwater value="true">
</applet>

The ROCKING parameter

Set to TRUE if you want the boat rocking.

If you set the "ROCKING" parameter to "TRUE" then you almost certainly need to reduce the height of the applet.

<applet code=lake width=250 height=220>
<param name=image value="scenic.jpg">
<param name=rocking value="true">
</applet>

You will need to set the height of the applet by trial and error. Start off with the height equal to about 1.8 * height of original image. If you can still see a gap appearing at the bottom of the applet as the waves move backwards and forwards, then you should reduce the height a little.

I'd suggest you put the lake.class file in the same directory as the page on which it will appear. If you want to move it elsewhere then use the "CODEBASE" option to point to the appropriate directory.

Some implementations of Java will not allow you to put the .class file in one subdirectory and the image file in another. If the try it might cause a security exception.

How does the example applet above communicate with the images and controls around it?

Well for a start, if you are not using at least version 4 of Netscape or Internet Explorer, it won't be reacting at all. So if clicking on the images and the checkbox are either having no effect or producing an error, that will probably be the reason.

The HTML source for the above is:

<applet code=lake name=lake1 width=250 height=250>
<param name=image value="scenic.jpg">
<param name=href value="http://www.demon.co.uk/davidg/spigots.htm">
</applet>

<form>
<img src="sunset_button.jpg" onmouseup="lake1.setImageValue('sunset.jpg');">
<img src="city_button.jpg" onmouseup="lake1.setImageValue('city.jpg');">
<img src="scenic_button.jpg" onmouseup="lake1.setImageValue('scenic.jpg');">
<img src="clouds_button.jpg" onmouseup="lake1.setImageValue('clouds.jpg');">
<br>
<input type=checkbox value="Rocking on" onClick="lake1.toggleRocking();">Rocking
<br>
<input type=checkbox value="Underwater on" onClick="lake1.toggleUnderwater();">Underwater
</form>

There are two important points to note in this code. Firstly, the <applet...> tag has been given a "name" attribute. Secondly, the different image and checkbox controls call methods as if the applet were a form or a text box on the web page. In fact the applet has become part of the browser's object model.

So - what are lake's methods?

setImageValue(var x)

setImageValue changes the image that is currently being reflected in the lake. The variable x should the name of a JPG or GIF file accessible by the applet.

setOverlayValue(var x)

setOverlayValue sets the filename of the overlay image.

setTargetValue(var x)

setTargetValue sets the target frame of the applet's "href" parameter.

setHRefValue(var x)

setHRefValue sets the hyperlink destination for when the applet is clicked.

setRockingValue(var x)

setRockingValue sets whether the applet is rocking or not. The value passed should be either "true" or "false".

toggleRocking()

toggleRocking sets the rocking on and off alternately.

setUnderwaterValue(var x)

setUnderwaterValue sets whether the image is viewed from underwater or not. The value passed should be either "true" or "false".

toggleUnderwater()

toggleUnderwater sets underwater viewing on and off alternately.

Blank applet

If the applet remains blank when it is run off the server and never shows the image, the chances are there are problems with the image. If the image is too large then it may not be able to create the animation in memory. On the other hand, it may be that the image is not accessible. Have you spelt the image filename correctly in the

<param name=image...>

line? Again you will need to check the case and also the file permissions.

Gap at the bottom

If you make the applet too large then you will notice a blank strip appear at the bottom of it as the waves lap backwards and forwards. The solution is to make the applet a bit smaller...

Positioning the horizon

On an artistic note, it is not a good idea to use an image that already has a horizon. If you look across the surface of a lake you will not see the horizon reflected in the surface. The best solution is to cut the image *at* the horizon.

It's turned upside-down!

Do not use transparent GIFs with the applet's "image" parameter. There is no problem using transparent GIFs for the overlay parameter - in fact this is recommended. You can usually tell if a transparent GIF has been used because the top half of the applet will have parts which appear to be upside down.

Why won't the applet work off my hard disk?

Some web browsers have trouble opening applets straight from a hard disk. I have noticed this happen with Internet Explorer 3 and Netscape 4. Once you have loaded the class file and the web page onto your web site you should find it works OK.

Why does my web page say "Class Format Error"?

Class files are binary files, just like image files are. Binary files contain more information than text (also known as ASCII) files do. If you transfer class files as if they were ASCII files then they will lose this extra information and will become corrupted. How do you transfer class files as binary files? You should transfer them in the same way that you transfer image files.

Why does my web page say "Class Not Found"?

This is a very common problem. It may be because of one of the following:

1. You have not put the class file onto the web site
2. You are not calling the file with the correct name (rename to use the same combination of upper- and lower-case letters as your class file)
3. Your transfer program has changed the name. This does happen. Some programs will shorten the ".class" extension to ".cla". Other will change the case of the letters to either all uppercase or all lowercase. See if you can change the options on the transfer program to stop it doing this.
4. You have include a "codebase=…" clause inside your <applet…> code in your web page. "codebase=…" tells the browser to look some place else for the class file.
5. Some other reason I haven't thought of :-)

    <a href="http://www.demon.co.uk/davidg/spigots.htm" target="_top">
    <img src="dglogo.gif"
          width=88 height=31 border=0></a>

It will put a little button on your page that will link through to my Java Spigots page.

It is only a request: feel free to omit it.

There are additional notes available for this applet at The Lake Applet: Notes

Remember that if you are transferring the .class file to another machine with FTP, you should set the 'binary' mode on. Failure to do so will corrupt the file and give rise to a "Class Format" error.

If you still have trouble getting the applet to work and you have tried all of the possible solutions listed above, then feel to contact me, remembering to include:

These two pieces of information will make it a lot easier for me to solve the problem. I cannot guarantee that I will be able to respond to all messages (there's only so many hours in the day...) but sending the URL of a page that doesn't work will greatly increase the chances of getting an answer.

Remember to keep a look out at my web site for new applets.

David Griffiths,

16/03/1999