Thread: [Jython-users] Re: [Jython-dev] new, trouble w/ simple applet

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[Mark]

>I am teaching a simple introductory course on programming. I am using
>Python and am interested in introducing at the end for interest sake the
>ability to create simple little programs running inside a browser.
>
>I am a bit clueless about Java.
>
>I have CLASSPATH set to:
>
>[mt@galois applet]$ plecho $CLASSPATH
>/home/mt/external/jython-2.1a1/jython.jar
>.
>./jpywork

>/home/mt/external/jython-2.1a1/Tools/jythonc
>/home/mt/external/jython-2.1a1
>/home/mt/external/jython-2.1a1/Lib

These last three entries isn't necessary.

>I have the following HelloWorld.py file:
>
>from java.applet import Applet
>
>class HelloWorld(Applet):
>    def paint(self, g):
>        g.drawString("Hello from Jython!", 20, 30)
>
>Running jythonc -J deprecation HelloWorld.py
>produces a class file with 9 deprecated API warnings.
>
>I have the following html file:
>
><html>
><body>
><center>
><applet code="HelloWorld.class"
>    width = 500
>    height = 105>
></applet>
></center>
></body>
></html>
>
>The environment that netscape has does contain the same CLASSPATH
>variable (this is required right?).

Not sure. It is certainly different from the setup used on the applet
demo pages: http://www.jython.org/applets. There we make a .jar file
that contains all the needed files including the core python files. As a
result no CLASSPATH setup is required but the html must then include a
line like:
   ARCHIVE="helloworld.jar".

>Here is the java console output:
>
># Applet exception: exception: java.lang.NullPointerException: trying to call makeJavaPackage(Ljava/lang/String;Ljava/lang/Str
>java.lang.NullPointerException: trying to call makeJavaPackage(Ljava/lang/String;Ljava/lang/Str
>  at org.python.core.PySystemState.add_package(PySystemState.java:504)
>  at org.python.core.Py.initProperties(Py.java:701)
>  at org.python.core.Py.initProxy(Py.java:719)
>...
>
>What the hell does this mean????

Not sure. This is the first time I have seen this message. I'm guesing
the stacktrace is a bit bogus. Applets are wellknown for reporting
errors that does not reflect the real problem ...

>I am using Jython 2.1a1 and JDK (from Sun) 1.3.1

... and I believe 1.3.1 is the real problem. Even if it isn't, I
strongly doubt you can make java1 applets with a java2 JVM. You will
need to get hold of and install a JDK1.1 and use that when running
jythonc.

>For interest sake here are the warning from jythonc:

These warnings are not important. We could make them to away but the
alternatives does not run as fast.

>Anybody have a clue as to what I am doing wrong?  I have tried copying
>the HelloWorld.class all sorts of different places.  I have tried
>calling the .class file in the html file different names like HelloWorld
>or jpywork/HelloWorld.class jpywork.HelloWorld - pretty much every
>conceivable combo.
>
>This applet is working for me at http://www.jython.org/applets the

Then I suggest you try to reproduce the way I built the applet demoes.

See the "Example" section on http://www.jython.org/docs/jythonc.html

>source of the html there is exactly what I have.

Not quite, the tag used on the applet demo pages look like this:

<APPLET CODE="HelloWorld" WIDTH="160" HEIGHT="50"
	ARCHIVE="appletdemo.jar" 
	NAME="HelloWorld"
	ALIGN="BOTTOM" 
	alt="This browser doesn't support JDK 1.1 applets.">
 <PARAM NAME="cabbase0" VALUE="appletdemo.cab">
 <H3>Something has gone wrong loading this applet.</H3>
</APPLET>

You need the ARCHIVE attribute for netscape (atleast for the windows
version) and the 

  <PARAM NAME="cabbase0" ..>

tag is needed for older IE browsers. Newer version of IE uses the
ARCHIVE attribute instead.

regards,
finn