JRE version affects portability

[Yvan]

I did an experiment friday morning where I burned my custom app to a
cdrom and then tried to get it to run off the cd on my PC at work, and
I got database errors that read something to the effect of.. "The
software version used to create the database might have been a
different version". I then tried copying all the files to my work PC's
hardrive and running it from there, .. but I got the same error
message.

I suspect that the version of JRE that's installed when derby databases
are created must also be present on whatever other machines you try to
run the app off of. For example, on my work PC, I have j2re1.4.2_05
installed, whereas on my home PC (where the derby database was
initially created, I'm running jre1.5.0_02. I guess this goes to show
that JRE is not backwards compatible. Anyone else run in to this
problem? Is this only specific to version 1.5.x, .. or are the 1.4.x
versions also not backwards compatible?

thanks,
- yvan

[Phil Cruz]

Java 1.5 is relatively new and several of the components are probably not supported on that version yet. This is one reason to bundle a JRE 1.4 with your application rather depending on the installed JRE of the client machine.

-Phil

[Yvan]

That's kind of what I figured. But on my machine, it seems that I
have several different version of JRE installed:

j2re1.4.2_03
j2re1.4.2_05
j2re1.4.2_06
jre1.5.0_02

Are each of these actually installed and independent of one another?
Or does the main java engine just get updated whenever a newer version
gets installed?

- yvan

[Phil Cruz]

I don't know what you mean by "main java version" but yes you can have multiple versions of the JRE on one machine that are independent of each other.  The "default" version will be the one that JAVA_HOME is pointing to, i.e the one that gets run when you type "java" at a command line.  However, a program can still bundle it's own JRE as well (like CFMX and BD do).

-Phil