macos - How is the Eclipse JDK setting affecting the system's JDK setting

Question

I was trying to compile a Grails application referencing third party JARs on Mac OSX. Although my system's JRE and JDK is set to Java 1.6 I always got a Compilation error: java.lang.UnsupportedClassVersionError: Bad version number in .class file when accessing classes in the JAR. Also when testing an existing Grails app the default stats of the app where showing that it's running with Java 1.6. So I really didn't have more ideas than to try to change the Java settings in Eclipse - I thought that's stupid as I'm not using Eclipse for the devlopment of this application - but voila - now the compilation of my app on the command line works just fine!

Can anyone explain me what Eclipse is doing here behind the scenes? I've had set the JAVA_HOME manually before with no effect.

Answer 1

The JDK (JAVA_HOME) used to launched eclipse is not necessarily the one used to compiled your project.

To see what JRE YOU y can select for your project, check the preferences

General > Java Installed JRE

By default, if you have not added any JRE, the only one declared will be the one used to launched eclipse (which can be defined in your eclipse.ini).
You can add any other JRE you want, including one compatible with your project.

After that, you will need to check in your project properties (or in the general preferences) what JRE is used, with what compliance level: