Setup eclipse + svn - eclipse

Question

I've got a Java project versioned by svn and trying to configure the build for linux. On my work computer all works fine and I committed the changes. To both my home computers however I get this error which seems like some trivial setup problem:
Exception in thread "main" java.lang.NoClassDefFoundError: adventure/Adventure
Caused by: java.lang.ClassNotFoundException: adventure.Adventure
at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
Could not find the main class: adventure.Adventure. Program will exit.
Did I forget to add the src to some path? The way it looks in ubuntu is here:
It was committed with Java 7 but on the ubuntu I have only Java 6. Could it still work or do I need to completely harmonize Java versions?
Update
I cleaned the build path and set up the JARs again and I'm going to add the Java 6 JRE since I don't use any Java 7 specific features so it should work if I only get the JRE set up. But I don't know how to add my JRE with linux? I can try also with windows and then maybe I can add a suitable JRE. Now there is a build problem:
Thanks but now I have no JDK which looks like the main problem and just a build problem:
Exception in thread "main" java.lang.Error: Unresolved compilation problem:
String cannot be resolved to a type
at adventure.Adventure.main(Adventure.java:74)
My Java version seems well though:
$ java -version
java version "1.6.0_24"
OpenJDK Runtime Environment (IcedTea6 1.11.1) (6b24-1.11.1-4ubuntu3)
OpenJDK 64-Bit Server VM (build 20.0-b12, mixed mode)
The installed JRE is OpenJDK 6 that should work:
My classpath variables look like this

Answer 1

Usually Java projects should be committed without the bin folder (set it to ignore).
It looks like your project was checked-in including the compiled class files from Java 7 with of course can not be loaded by Java 6.
You should proceed as follows:
Open a terminal and change into your project directory
execute svn delete bin
execute svn propset svn:ignore bin .
Does anybody how to do this from whithin Eclipse?
Switch back to Eclipse and execute "Clean" command on the project so that Eclipse re-builds it using your Java version.

Answer 2

But I don't know how to add my JRE with linux?
You surely know Preferences->Java->Installed JREs. Please browse for your Java installations in usr/lib/jvm sub directories.