[news.eclipse.newcomer] Re: Compiling for older version of java

[Mark Dexter <dextercowley@xxxxxxxxx>]

Ed Merks wrote:
> Joel,
>
> I didn't think that Java 6.0 changed the class version levels again like 
> Java 5.0 did.  Java 5.0 changed the language significantly so there is 
> additional information about generics that needs to be encoded in the 
> .class files, but I didn't think Java 6.0 had any such impact.  So my 
> suspicion would be you are actually trying to run with a 1.4 JRE when 
> you are getting the error you reported.  You could try setting your 
> language level to 1.4 to confirm that...
>
>
> joel wrote:
> > Olivier Thomann wrote:
> >
> > > This means you didn't install a JRE 1.5, so the jre 1.6 is picked up 
> > > instead of a 1.5 one.
> > > I recommend that you add a JRE 1.5 in the Preferences>Java>Installed 
> > > JREs
> >
> > Ok, so what you are saying is that setting the 'Execution Environment' 
> > to J2SE-1.5(jre1.6.0_02) without actually having the JRE 1.5 installed 
> > will not work as I expected to?  I was trying to avoid needlessly 
> > installing another version of the JRE.
> >
> > --Joel
I may be missing something, so I apologize if that is the case. In my 
limited experience, (a) you shouldn't need to install the 1.5 JRE or JDK 
to compile with a lower compliance level; (b) if you compile with a 
compliance level that is too low for the classes being compiled, you do 
get compiler errors; and (c) you do need to compile with a lower 
compliance level to run on a lower level JRE.

I have a small test project that uses generics, so it requires 1.5. If I 
change the compiler compliance to 1.4, it doesn't compile. I have 1.6 on 
my Windows machine and 1.5 on my Linux machine. If I compile at the 
default 1.6 compliance level on Windows, it won't run on my Linux 
machine. If I recompile with 1.5 on Windows, it does run on the Linux 
machine. I did not need to install 1.5 on my Windows machine.

So I think that is how it is supposed to work. Why it is not working in 
this case I don't know. I have done this with Eclipse 3.3.0 but not with 
3.3.1. Hope this helps. Mark