I try to make swt based application using Eclipse 3. After reading tutorial, I got this error when I launch the program. I think I have set up the project properly.
Exception in thread "main" java.lang.NoClassDefFoundError: org/eclipse/swt/internal/gtk/OS
at org.eclipse.swt.internal.Converter.wcsToMbcs(Converter.java:63)
at org.eclipse.swt.internal.Converter.wcsToMbcs(Converter.java:54)
at org.eclipse.swt.widgets.Display.<clinit>(Display.java:118)
at SWTHello.main(SWTHello.java:5)

When I build the program, it is ok. So what's the problem?

you don't have all of the SWT jar files you need in the class path to run the application (this may be a longer list than the jars needed to compile it)... make sure all of the SWT libraries are in the working space's build path (it's in properties for the project)