Wednesday Sep 02, 2009

java.lang.NoClassDefFoundError: com/sun/javafx/runtime/FXBase

I created a simple JavaFX applet and compiled it with "javafxc" and created a jar "HelloApplet.jar". Then, I created a simple HTML file as follows:

<script src=""></script>
               archive: "HelloApplet.jar",
               draggable: true,
               width: 150,
               height: 100,
               code: "hello.HelloApplet",
               name: "HelloApplet"

When viewing the HTML, I did not see the expected applet content in it - just a gray rectangle panel :-( Then, I turned on the "Show Java Console" option. I saw the following exception trace in Java console:

JNLPAppletLauncher: static initializer
Exception in thread "AWT-EventQueue-2" java.lang.NoClassDefFoundError: com/sun/javafx/runtime/FXBase
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(
[.. more stack frames deleted for brevity ..]

Aha! com.sun.javafx.runtime.FXBase is new since JavaFX 1.2. Yes, I had compiled my applet with JavaFX 1.2 (full version "1.2.0_b233"). So, the JavaFX runtime used turned out to be old one! I changed the HTML script URL from to The applet worked as expected :-)

Tuesday Jul 28, 2009

My twitter updates..

In the past, I blogged about Cricket (the sport and not the insect!) in this space. Once angry reader questioned me why I was writing that here. I guess people read my Sun blogs only tech. stuff. That is fine. So, I've revived my twitter login. I'll be posting my one liners (tech as well as non-tech) there. Longer posts on tech. (mostly Java, JavaFX) topics will continue here.

Tuesday Jul 21, 2009

Teaching programming to kids

I've been experimenting/playing with programming tools for kids. I've two kids - 8 and 5 year old.


Great multimedia rich introduction to programming for kids. My son keeps playing with it! If you are after ease-of-use, this is probably the best choice. Available for download on Mac and Windows. If you have Squeak installed, you can get Scratch running on Linux as well (possibly with some audio problems). It is possible to export your Scratch projects as applets from your website

  • Website:
  • Tutorials:
  • Examples/Repository: Register @ to download lots of great samples! You can view scratch programs online if you have Java plugin installed.


EToys is an tool to teach children a multimedia rich authoring environment and visual programming system. If you have OLPC laptop (or emulation environment for OLPC), it comes pre-installed with EToys. Or else you can download EToys for your platform. It is avaliable for Linux, Mac and Windows.


Although StarLogoTNG is described as "tool to create and understand simulations of complex systems", it can be used as a tool to teach programming. It supports 3D and it is cross-platform a (Java) tool.


This is an environment to teach programming in a 3D environment. This is a cross-platform (Java) tool.

Turtle Art

Turtle Art activity is bundled with OLPC. If you don't have OLPC, you can use an emulator environment. For example, you can download VirtualBox and run OLPC inside it following the steps here. I run VirtualBox on Mac, Ubuntu and Windows XP.

Want to work with source code?

So far, we looked at visual programming tools. But, if you think it is better to expose to source code ("they have to look at code at somepoint anyway, let them see syntax errors sooner"), then you may want to try these:


From the site: "Greenfoot as a combination between a framework for creating two-dimensional grid assignments in Java and an integrated development environment (class browser, editor, compiler, execution, etc.) suitable for novice programmers". This is a cross-platform (Java) tool.


With Bots Inc we can learn how to program robots interactively. Language used to program is Smalltalk (BotsInc is built with Squeak). Since BotsInc is a Squeak image, it possible to slowly graduate to full Smalltalk. It is available on all platforms.

Alice 3 Beta

Alice 3 beta is hosted at Alice 3 beta seems to have support to emit NetBeans projects. I've played with Alice 3 Beta - but not yet with NetBeans project support.

Tuesday Jul 14, 2009

BTrace "unsafe" mode

We kept saying BTrace is a safe, dynamic tracing tool for Java. To ensure safety, BTrace does not permit many constructs of Java language and also allows calls only to BTraceUtils class.But, not everyone likes safety -- sometimes developers want "unsafe" facility ("I know what I am doing"-style). We have got comments of this nature about BTrace - for example here and here. We have added "unsafe" mode to BTrace - you can edit "btrace" script to change -Dcom.sun.btrace.unsafe=false to -Dcom.sun.btrace.unsafe=true. In "unsafe" mode BTrace permits all Java constructs and also allows calls to arbitrary code. Like every other unsafe facility in programming, you are on own your own with this facility! You may get weird errors while instrumenting target classes and/or running transformed code. But then you know what you are doing, right?

Monday Jul 13, 2009

javafxdoc-style docs for Java code

You may have browsed JavaFX API docs generated by javafxdoc tool. javafxdoc tool is implemented as a doclet. It is possible to use javafxdoc's doclet to generate API docs for Java code.

Note: The XMLDoclet implemented as part of javafxdoc tool is an implementation detail and not part of official JavaFX/tool API and so please do not depend on this. This is more for fun/learning/personal use!)

I generated javadoc for BTrace source using the following command:

javadoc -docletpath $JAVAFX_HOME/lib/shared/javafxdoc.jar  -doclet -sourcepath .  -subpackages com.sun.btrace

where JAVAFX_HOME is the directory where JavaFX SDK lives.

A screenshot from generated docs:

Monday Jul 06, 2009

BTrace project moved to

We have recently moved BTrace project to If you are interested in BTrace, please continue to use it and help develop it from

Thursday Feb 26, 2009

Prizes for having fun! Hurry....

Do you live in India? What do you want? Sony Ericsson phone or Canon Camera or iPod? If so, have fun writing JavaFX code and win any of these prizes!

Monday Feb 23, 2009

JavaFX interactive shell

JavaFX compiler has a built-in script shell - Per Bothner has implemented a read-eval-print loop facility for JavaFX. The script shell class is Note:This is in the openjfx-compiler repository and not in the JavaFX 1.0 binary.

A sample JavaFX session is as follows:

$ java -cp dist/lib/shared/javafxc.jar 
/\*fx1\*/ "hello"
/\*fx2\*/ 2 + 4
/\*fx3\*/ function greet (name) { println("Hello, {name}") }
/\*fx4\*/ greet("Sundar")
Hello, Sundar
/\*fx5\*/ var s = [ "Sunday", "Monday", "Tuesday" ]
[ Sunday, Monday, Tuesday ]
/\*fx6\*/ for (i in s) println(i) 
/\*fx7\*/ class Person { public var name: String; }               
/\*fx8\*/ var p = Person { name: "Sundar" }
/\*fx10\*/ import javax.swing.\*;
/\*fx11\*/ var f = new JFrame("hello");
fx11:1: cannot find symbol
symbol  : class JFrame
location: class fx11
/\*fx13\*/ var f = new javax.swing.JFrame("hello")
/\*fx14\*/ f.setSize(300, 300)
/\*fx15\*/ f.setVisible(true)

While there is a generic shell called "jrunscript" for languages that implement jsr-223, it does not work very well for statically typed languages (which can be said about jsr-223 itself). But, the above mentioned JavaFX script shell is independent of jsr-223 interface.

Besides, jrunscript crashes for JavaFX!

$ jrunscript -cp dist/lib/shared/javafxc.jar -l javafx
fx> "hello"
Exception in thread "main" java.lang.NoSuchMethodError:$OptionHelper;)[Lcom/sun/tools/javac/main/JavacOption$Option;
	at javax.script.AbstractScriptEngine.eval(

This is because JavaFX compiler code depends on modified javac classes. The code for jrunscript lives in tools.jar along with the unmodified javac classes! These unmodified javac classes are loaded which results in exception from javafxc code! We have to use the bootstrap path workaround as shown below:

$ jrunscript -J-Xbootclasspath/p:./dist/lib/shared/javafxc.jar -l javafx
fx> 233 + 334
fx> for (i in [0..4]) println(i)

But, now we have a much better ScriptShell for JavaFX :-) We don't need to resort to this hack...

Friday Feb 20, 2009

A JavaFX compiler debug trick

There is an unsupported (read - can be removed in future without notice!) command line option with JavaFX compiler. If you run javafxc as

    javafxc -XDdumpjava Test.fx

the compiler generates intermediate Java code for your JavaFX program in "./dumpjava" directory (compiler expects you to create ./dumpjava directory before invoking javafxc). This is meant to be a debugging option for JavaFX compiler developers. But, you can look at generated Java code to see what happens behind the scenes - much like C++ programmers used to look at intermediate C code and/or preprocessed code.

JavaFX for Java, JavaScript programmers

I missed attending and speaking at Sun Tech Days at Hyderabad due to a personal reason :-( In fact, I prepared slides for a talk titled "JavaFX for Java, JavaScript programmers". This is much like my earlier language comparison blog entries such as Java, JavaScript and Jython, Java, Groovy and JRuby etc. The idea is to learn a language by language comparison - and not to conclude "better"/"worse" language and so on. So, no politics please :-) Although I could not attend Sun Tech Days, I am posting the slides here : slides in a .pdf file

Tuesday Dec 23, 2008

Installed Ubuntu 8.10 on my PS3

Ubuntu on PS3

I wanted to install Ubuntu on my PlayStation 3.

My Setup

  • PS3 is NTSC 60 GB hard disk version - updated with firmware version 2.42.
  • PS3 is connected to 32 inch 720p Sony LCD TV via HDMI.
  • PS3 is connected to wireless network.

Stuff needed in addition to the above

  1. USB keyboard.
  2. USB mouse.
  3. CD burned with Ubuntu powerpc iso (ubuntu-8.10-alternate-powerpc+ps3.iso).

Preparing PS3

  1. Backup your PS3 hard disk using [Settings] -> [System Settings] -> [Backup Utility] menu. I didn't bother to backup the hard disk.
  2. Go to [Settings] -> [System Settings] > [Format Utility] menu.
  3. Select [Format Hard Disk] and click [Yes].
  4. Choose [Custom] and [Allot 10GB to the Other OS].
  5. Select [Quick Format] and confirm with [Yes].

Installing Ubuntu

  1. Connect USB keyboard and mouse to PS3.
  2. Insert the disk with Ubuntu iso image into PS3.
  3. Go to [Settings] -> [System Settings] > [Install Other OS]. PS3 will detect the install CD and copy files and instruct you to ..
  4. Select [Settings] -> [System Settings] -> [Default System] -> [Other OS]. This will boot PS3 with other OS. From then onwards, follow the Ubuntu installation instructions.

Small hiccup

The installation was smooth except for one small issue - the installation seemed to hang in "Select and install software" step. After 6% the progress bar did not increase at all! Fortunately, this seems to be a known issue with text mode installer. Please refer to Ubuntu 8.10 release notes and bug 290234. I pressed Alt-F4 and Alt-F1 to toggle between logging console and main screen to check the progress. Eventually, the installation completed! While installing I configured network as well -- i.e., giving WEP password etc. -- not sure if this is mandatory, but in my case I have wireless connectivity and so I supplied the configuration values for the same.

Switching between Operating Systems

  • From Ubuntu to Game OS, use the command
        sudo boot-game-os
  • From Game OS to Ubuntu, use the menu
       [Settings] -> [System Settings] -> [Default System] -> [Other OS]

Few Screenshots

Wednesday Dec 17, 2008

Debugging option for javac and javafxc

I work on JavaFX compiler these days. The command line (debugging) option that I often use is -doe ("dump on error"). This option prints stack trace of the compiler when error message is printed. NOTE: This is an internal option and can be removed any time without notice! But, it is useful for debugging. This option works for javac as well as javafxc. When I misspelled "class" as "clas" and run compiler with -doe option, I got the stack trace below:

$ javac -doe class, interface, or enum expected
clas t {}
1 error

Wednesday Dec 10, 2008

Yet another reason for using VirtualBox

I bought a laptop from ELCOT for my sons. It came with SUSE Linux Enterprise Desktop 10 SP2. Kids wanted to see how it is like playing games in the "old" days. Nothing better than seeing and really playing! And so VirtualBox :-)

Also, having access to more than one OS without having to partition does not hurt -- even for a kid's laptop! We can run OLPC, OpenSolaris, Puppy Linux, or anything else!

Thursday Dec 04, 2008

Playing with Alice and PhET

These days, my son is playing with these (apart from usual game sites):
Alice is a 3D programming environment. He likes it as much as he likes Scratch.
Interactive simulation tool for physical phenomena from University of Colorado. He kept trying to soft land "on the moon" :-) I guess Chandrayaan I has impressed him a lot!

What is the common between Alice and PhET apart from being great education tools? It is Java! With the advent of JavaFX, we can expect that such fantastic rich GUI applications will be written in JavaFX.

Friday Aug 08, 2008

Scriptifying BTrace?

One of the issues reported with BTrace is that the trace authors have to write "verbose" code [some people say Java is "verbose"!]. In BTrace, we have to repeat the same set of imports, annotations in every btrace file and all methods have to be "public static void" and so on. Instead of inventing a new scripting language, I've added a simple C preprocessor like step in BTrace compilation. This preprocessor is based on the one in the GlueGen project. Thanks to Ken Russell for this code and for reviewing my changes specific to BTrace project. The preprocessor solution does not rule out a scripting solution in future :-) If you have nice ideas or would like contribute in this area, you are always welcome! But, I think preprocessor solution is simple and will be useful to some.

Simple Example:


To run this sample, the following command can be used:

   btrace -I . <pid-of-the-traced-process>

Without the -I option in command line, BTrace skips the preprocessor step.



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