Sunday, January 17, 2010

Ruby and AOP

Right now I am learning Ruby, I focus on Dave Thomas' famous pickaxe Ruby book, last week I just finished the chapter 24: "Metaprogramming".Now I learn the power of Ruby Metaprogramming, right now it is still quite difficult for me, I am sure I will read this chapter over and over in future.

Today I want to discuss my impression of AOP concept in Ruby.
I learned AOP from java, in java you have to use AspectJ or Dynamic Proxy implement AOP. But comapre to Java, I realize Ruby support AOP in the lanuage level:
  • Classes are open: you add new method or attribute for any existing class, or replace the method with new one.
  • Module and Mixin: you can easily add new functionalities by Mixin the module.
  • MetaProgramming: you can dynamically define a method on the fly, using hook method as call back, easily implement before, after and around advice
I feel by using the above technologies, it is quite easy using AOP concept in Ruby, for example you can easily implement a Logging Aspect in a Module, then get it mixin in your application code.That is separating of concern, which is the essence of AOP.
So I will say AOP is built in support in Ruby language level.

Today I found a blog called "Does Ruby need AOP?", the author argue that Ruby metaprogramming is not AOP,because he think AOP is all about semantics, while Ruby metaprogramming is too low level. I feel this argument is too academic, from the pragmatic perspective, I think as long as Ruby can do the job of separation of concern, then it is AOP, then who care about the semantics?

Here are some useful links:
  1. another blog about ruby and APO at 4 line of code
  2. slide: AOP of Ruby

Sunday, January 10, 2010

Customize Your J2ME Emulator

Why do we need to customize J2ME emulator ?
As a J2ME mobile developer, you have to port application to different devices,  while the J2ME default emulator only provide 4 different profiles, which can not meet our needs, and also some platforms like BlackBerry, Nokia S60 etc, the J2ME emulator they provided are really slow to launch, which is really inconvenient. If you can customize the emulator to support the device you are porting, which will improve your developing productivity.

Here I will give you’re my examples: BlackBerry 9000(Bold), LG XENON, Nokia 5800, Samsung Brooklyn. Please check the following table for their specs:
Device Name
Key pad
Screen Size
Touch Screen?
Black Berry 9000
Nokia 5800
Samsung Brooklyn

I will show you how I customize the above 4 devices.

Where are the emulator device profiles located?
 For example, if you installed wireless toolkit 2.5 in c:\WTK25, then the device folder is:

The mobility package is included in the NetBeans 6.5 or later version, the wireless toolkit folder is like this:
C:\Program Files\NetBeans 6.x\mobility8\Java_ME_platform_SDK_x.x

Create a new emulator device profile
I like to choose Sun Wireless Toolkit 2.5, because its Qwerty Device emulator looks better.   For example, if I want to create a device for Black Berry 9000:
1.  Copy the entire folder of  “QwertyDevice” to a new folder, rename the new folder name to “BlackBerry9000”
2.  Go inside the folder, rename the Qwerty.properies file to

Enable the touch screen
The touch screen feature is disabled for J2ME default emulators. If you want to enable it, you need to modify the .properties file. In properties file, find following statement:


Change false to true will enable the touch screen.

Change the screen size
For example, for BlackBerry 9000, its screen size is 480x320, then go to .prperties file, update the following values:


    and ..

Please note that you need to make sure:
   screen.height >  screenPaintableRegion.height + screenPaintableRegion.y
   In the properties file, screenPaintableRegion.y=11, so the screen.height value is 332.

   If you don’t put the correct value, the emulator will throw exception once it is launched.

Make your customization available in NetBeans IDE
Once You finished the customization, you need to update your NetBeans IDE environment:
  1. Select Tools – Java Platform,  choose Sun wireless toolkit 2.5, click Refresh button
  2. You will see the device names  you added in the device folder

Here are the examples:

BlackBerry9000: 480x320

LGXENON: 400x240

Nokia 5800: 640x360

Samsung Brooklyn: 320x240

You can easily customize J2ME emulator by modifying the .properties file, even it is really simple, it can improve your productivity considerably.

Further steps
This article is only focused on Wireless Toolkit 2.5.x , Sun released the new wireless toolkit 3.0,  the device emulators are changed a lot. I need to do more investigation on 3.0 emulator in future..