Check wich version of the Java you are using

Always know which verison of the JDK you are using, if you switch programming computers:

I written a Java GUI program on Windows server 2008 platform and was planning to show it to my adviser on my Mac book.
After I imported the project into Eclipse, it gave me some error information, the GroupLayout can not be found.
By doing a little research I found that the GroupLayout is not in Java 1.5.  According to this I changed the default jdk from 1.5 to 1.6. Then everything is back to normal.