I have both jre 6 and 7 installed in my machine (with Windows 7). The default jre for my workspace is 6, and all my projects reference to the workspace default jre. So far so good, everything works fine. But if I change the system variable JRE_HOME to the location of jre 7, I keep getting NoClassDefFoundError for random classes when running my application.
Why does this happen? I don't want to know how to solve it, I want to know why does it happen.