The followings are what I'm doing.

1. Don't define java.home by yourself. Ant USES an internal one derived from your ENVIRONMENT var JAVA_HOME. It is immutable.
2. I do the followings:
* In my build.properties (READ first)
jdk13.bin=${tools.home}/jdk1.3.1_13/bin
jdk14.bin=${tools.home}/j2sdk1.4.2_08/bin/
* In my MASTER properties file (read last), set default javac.location=${jdk13.bin}
* In my prj.properties, if I NEED to use 1.4
javac.location=${jdk14.bin}
* in my javac task
executable="${javac.location}/javac.exe"

The followings are what I'm doing.

1. Don't define java.home by yourself. Ant uses an internal one derived from your environment var JAVA_HOME. It is immutable.
2. I do the followings:
* In my build.properties (read first)
jdk13.bin=${tools.home}/jdk1.3.1_13/bin
jdk14.bin=${tools.home}/j2sdk1.4.2_08/bin/
* In my master properties file (read last), set default javac.location=${jdk13.bin}
* In my prj.properties, if I need to use 1.4
javac.location=${jdk14.bin}
* in my javac task
executable="${javac.location}/javac.exe"