alvin's blog

DOS batch files to compile and run a Java program (and create a jar file)

This isn't the most high-tech way to do things, but I thought I'd share these Windows (DOS) shell scripts that I'm currently using to compile a Java application, create a Jar file to distribute the application, and finally run the application. I ended up creating these scripts because of configuration problems on my Windows PC, but I thought they might be useful samples for others.

java.lang.UnsupportedClassVersionError (UnsupportedClassVersionError)

You know what will really screw with your mind? When there is a 1.4.2 version of a java.exe file in the C:\Windows\System32 directory of your Windows XP system, and you're trying to compile and run a Java 1.5 program from the command line. I kept getting this error message and couldn't figure it out, even though I knew what it meant(!):

A JRuby program that runs the Java Robot class

This is just my second JRuby program, but I thought I might as well go for the gusto. This Ruby/JRuby program creates an instance of a Java Robot class (java.awt.Robot), then moves the mouse to a position where it clicks the Minimize button on a full-screen window (assuming a display resolution of 1024x768). Warning: if you have something else in that location it will click that instead!

Here's the Ruby/JRuby code:

Great design, the user experience, and designers

(Note: This article was originally written in 2005.) As far as design goes, products like the Mac, TextMate, and JFormDesigner have really opened my eyes to the possibilities of great design, and it's impact on people (I was going to say "users", but that say more inhuman than ever before), and my personal feelings about using these products. At the moment I don't really ever want to go back to using a Windows PC ever again, in spite of the few things I don't like about Mac OS X.

How to print a Ruby hash sorted by value

I recently needed to print the information in a Ruby hash, with the results sorted by value. Here's a general recipe on how to print the hash results sorted by value. I've created a sample hash, and populated the hash with sample data, to show how this works.

First, here's the sample code, using the first name of each person as the key, and the last name as the value of the key/value pair:

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