Debugging

JSwat's not bad.

How to connect a debugger to a running JVM: http://www.ncsa.uiuc.edu/UserInfo/Resources/Hardware/IBMp690/IBM/usr/idebug/help/en_US/debug390/tasks/tb3attjv.htm

XML Event-based Parsing

STaX

A "pull" approach where the application requests events from the parser. Need to check it out further. Intro at http://www.xml.com/pub/a/2003/09/17/stax.html .

Java per se is a proprietary product, but there are many free projects that aim to provide all (or part) of the Java environment as Free Software. http://www.dwheeler.com/java-imp.html lists many of those projects.

unit test: http://www.junit.org/ - "keep the light green to keep the code clean." I'm definitely test-infected, writing and running unit tests is becoming second nature.

Infrastructure

IBM JVM on Linux

IBM's JVM 1.4.1 for GNU/Linux doesn't seem to recognize old-style timezone names. My /etc/localtime was a link to /usr/share/zoneinfo/US/Eastern and the JVM would never use daylight savings - it was always GMT+5. When I changed the link to /usr/share/zoneinfo/America/New_York it worked fine. See http://www.mainframeforum.com/t590240.html which seems to be relevant despite being a mainframe forum.

public class date { public static void main(String[] argv) throws java.io.IOException {System.out.println(new java.util.Date()); }}

Profiling

Mike's Profiler - http://mjp.sourceforge.net/ looks promising, has actual documentation and the maintainer seems to be maintaining it on an ongoing basis. The GUI is easy to understand. Unfortunately it seems to run very slowly and crash before JBoss can fully boot up. NOTE - I need to test 0.06 which has a statistical sampling mode

JTreeProfiler - http://sourceforge.net/projects/jcoverage/ this one streams to an XML file on a per method invocation basis so it's probably unsuitable for anything but trivial profiling (booting JBoss wrote a 2.3GB file). The analysis GUI is interesting and very graphical but hard to make sense of.

JPerfAnal - http://sourceforge.net/projects/jperfanal/ can you think of a more unfortunate name for a performance analysis tool? In any case this guy seems to have the right idea in that he reads the stock Sun profiler output so he doesn't need a platform-specific library to gather data. Unfortunately his GUI is lame and there's not one word of documentation.

Extensible Java Profiler - http://ejp.sourceforge.net/

JMP - http://www.khelekore.org/jmp/ GTK GUI, written in C.

JRat - http://jrat.sourceforge.net/ takes an interesting approach - you "instrument" your code after you build.

XML Parsing

http://cafeconleche.org/books/xmljava/ - looks like a good starter book.

Java as of version 1.4 comes with a competent XML parser and XSLT transformer built in, but sometimes it's preferable to use a different one, for features or speed.

There are two ways that an application can get a parser so you need to either know which one you're trying to use or cover both.

SAX Parser

This is the old approach.

Property

• javax.xml.parsers.SAXParserFactory
  • org.apache.xerces.jaxp.SAXParserFactoryImpl - value to use for Xerces (xercesImpl.jar on the classpath)

Code

http://java.sun.com/j2se/1.4.2/docs/api/javax/xml/parsers/SAXParserFactory.html

XML Reader

This is the new approach.

Property

• org.xml.sax.driver
  • org.apache.xerces.parsers.SAXParser - value to use for Xerces

Code

http://java.sun.com/j2se/1.4.2/docs/api/org/xml/sax/helpers/XMLReaderFactory.html

				parser = XMLReaderFactory.createXMLReader();

Float sucks

Binary arithmetic (e.g. Java float) doesn't cut it when applied to money - it's not accurate on the right side of the decimal point. Java seems to have the answer in java.math.BigDecimal but from what I've seen on the web it's not a very good implementation.

IBM has proposed a replacement of the BigDecimal class, the website is at http://www2.hursley.ibm.com/decimalj/. The site does a great job of explaining why decimal arithmetic is better than binary and also has many interesting links. They also have an implementation available but it's under a very restrictive license, you can only use it for 90 days and then you must destroy it - there's no way to buy it, either.

The IBM page points to a commercial implementation of a BigDecimal class at http://users.belgacombusiness.net/arci/math/. It's not very expensive - 500 Euro (which is closer to $500 than those common-market pinkos would hope!). It claims to be fast and have good formatting features.

There was another implementation but it seems to have fallen off the net. Google had cached entries for a package called TCE/Java at http://www.voicenet.com/~hsk0/tce/ but it seems to have fallen off the net. The guy that wrote it is Howard Kapustein, maybe he'll show up again.

Misc Notes

IBM's JVM 1.4.1 for GNU/Linux doesn't seem to recognize old-style timezone names. My /etc/localtime was a link to /usr/share/zoneinfo/US/Eastern and the JVM would never use daylight savings - it was always GMT+5. When I changed the link to /usr/share/zoneinfo/America/New_York it worked fine. See http://www.mainframeforum.com/t590240.html which seems to be relevant despite being a mainframe forum.

public class date { public static void main(String[] argv) throws java.io.IOException {System.out.println(new java.util.Date()); }}

-- TobyCabot - 28 Dec 2001 - 24 Jun 2003

Arrays vs Collections

JRat - http://jrat.sourceforge.net/ takes an interesting approach - you "instrument" your code after you build.

Profiling

There are many expensive commercial tools for profiling Java programs while they're running, but since Java has the JVMPI interface pretty much anyone can hook into the JVM at run time and find out what's going on. This is another category of programs where there seem to be far too many half-baked efforts, but here are my notes from a few hours of fooling around with various tools.

JTreeProfiler - http://sourceforge.net/projects/jcoverage/ this one streams to an XML file on a per method invocation basis so it's probably unsuitable for anything but trivial profiling (booting JBoss wrote a 2.3GB file). The analysis GUI is interesting and very graphical but hard to make sense of.

JPerfAnal - http://sourceforge.net/projects/jperfanal/ can you think of a more unfortunate name for a performance analysis tool? In any case this guy seems to have the right idea in that he reads the stock Sun profiler output so he doesn't need a platform-specific library to gather data. Unfortunately his GUI is lame and there's not one word of documentation.

Random Musings

Why don't people use arrays in Java? It seems to me that people get so excited about Collection, Set, List etc that they forget about arrays. Arrays have some definite issues, but they also have some advantages. Arrays are fixed-length so they're not good if you're not sure how many things that you're going to put into them in advance. Their big advantage (which limits their use) is that they're strongly typed. This can be a big advantage in many cases, i.e. where you've got a bunch of the same thing. In this case an array is nice because it enforces type safety in a way that a Collection doesn't.

In summary, an array is the correct data structure to use where you have a known number of objects all of the same type.

Coding Conventions

Use Sun's http://java.sun.com/docs/codeconv/html/CodeConvTOC.doc.html and override what you feel is wrong. Personally, I feel that the 80 column constraint is too limiting; I prefer to allow people to use 132 column line widths.

When something is an identifier, and you feel that you must append "Id" in some form to the name, use ID not Id. It's easier to type and reflects that most people call it an "eye-dee" not an "id".

-- TobyCabot - 28 Dec 2001-31 May 2002

Java is extremely popular in commercial software development - it's dominant in the area that I work in: operations support software for communications companies. It's not at all popular in the Free Software community because it's a proprietary product owned and controlled by Sun.

The Java home page is http://java.sun.com/; you can download a developer kit or run-time from there. Java per se is a proprietary product, but there are many free projects that aim to provide all (or part) of the Java environment as Free Software. http://www.dwheeler.com/java-imp.html lists many of those projects.

Books

Bruce Eckels Thinking in Java

Nutshell

Development Tools

building: ant - "like make only without make's wrinkles"

modelling: argouml - a UML modelling tool that can generate Java skeletons.

debugging: jswat

database access: isql, squirrelsql

Infrastructure

tomcat - servlet engine, jboss - j2ee container, openejb - ejb container, avalon - server framework, maverick - presentation framework

Libraries

trace logging: log4j

Misc

Here's a cute hack to enable token substitution in java property files: http://www.sys-con.com/java/source.cfm?id=1228

Using Java on Debian GNU/Linux

$ gcj -C HelloWorldApp.java
$ kaffe -addclasspath . HelloWorldApp

-- TobyCabot - 28 Dec 2001-19 Mar 2002

-- TobyCabot - 28 Dec 2001