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Author Topic: EJS loading  (Read 5669 times)
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on: April 28, 2009, 01:09:51 am » posted from:Lansdale,Pennsylvania,United States

Hello again,


I have created couple of simulations using EJS and hoping to do more. Is it legal to display the simulations in my site?
Why is it taking this long to display the simulation?
I noticed that even in your forum, simulations take quite a bit of time to display. How can we improve this?

You can see my simulations at the following location.:


There are two simulations.  'Reflection and Refraction' and Simple Pendulum. First simulation will display, but it takes a lot of time to download. Second one has trouble. I did some modifications to the html files. I need to check those again.


Fu-Kwun Hwang
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Reply #1 on: April 28, 2009, 07:40:31 am » posted from:Taipei,T\'ai-pei,Taiwan

We have switched to EJS 4 two months ago. There are many new features available and it also required larger jar file.
The typical size of EJS is 1.2-1.4M Byte if data analysis/video/translation... tools are all available (which is the current setting).
It will be slow if you have slow connection. It took 8-10 s to fullly load jar file for my browser.
You can remove some of the setting to reduce the file size to about 0.7-0.8M.

It took me 25-30 seconds to load your first page. The following is the error message when I load your second page:
Can not find Simple_pendulum_pkg.Simple_pendulumApplet.class。
java.lang.ClassNotFoundException: Simple_pendulum_pkg.Simple_pendulumApplet.class
at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Unknown Source)
at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
at sun.plugin2.applet.Plugin2ManagerAppletExecutionRunnable.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.io.IOException: open HTTP connection failed:http://downloadanswer.com/Documents/Simple_pendulum_pkg/Simple_pendulumApplet/class.class
at sun.plugin2.applet.Applet2ClassLoader.getBytes(Unknown Source)
at sun.plugin2.applet.Applet2ClassLoader.access000(Unknown Source)
at sun.plugin2.applet.Applet2ClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
... 7 more

The jar tag in your applet is "Simple pendulum.jar" .

However, there is a space in your filename. Normally, I will create a file named as "Simple_pendulum".
Please reload your xml source "Simple pendulum.xml" , save it as "Simple_pendulum.xml" , compile it again and upload it to the server. This might solve your problem.
Please use only english alphabet ,number for your file name.  You can use underscore, but do not use " " (space) as part of file name.
Because EJS use your filename to name some of the class and variables.
I download your jar file and it is a corrupted jar. May be there are other problem!
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Reply #2 on: April 28, 2009, 07:55:13 am » posted from:SINGAPORE,SINGAPORE,SINGAPORE

Is it legal to display the simulations in my site?

Authors can distribute any simulation that they create using EJS, provided a reference to this fact is included, together with a link to the official Web page for EJS: http://fem.um.es/Ejs. It is not necessary to include this reference in all pages with a simulation on it of an educational unit. Including a reference for the whole set in a clearly visible place will suffice.

My thoughts:
Perhaps you should change "Created with Easy Java Simulations" to "Created with Easy Java Simulations with the link.? To help spread the use of Ejs!

In addition, it would be integrity of your character to guide you in your actions.
for example, if you use other authors source codes like Prof Hwang's,  This work is licensed under a Creative Commons Attribution 2.5 Taiwan License.

You are free:

  * to Share — to copy, distribute and transmit the work
  * to Remix — to adapt the work

Under the following conditions:

  *Attribution — You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work).

This varies from author to author so need to check with authors when in doubt?

Like mine is

Creative Commons License
This work is licensed under a Creative Commons Attribution 3.0 Singapore License.

You are free:

  * to copy, distribute, display, and perform the work
  * to make derivative works

Under the following conditions:

  * Attribution. You must give the original author credit.

Basically i same as Prof Hwang's.

But if you are more restrictive to sharing, there are others licenses like

Creative Commons License
This work is licensed under a Creative Commons Attribution-Share Alike 3.0 Singapore License.
« Last Edit: April 28, 2009, 08:17:22 am by lookang » Logged
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