Hi,I'm a new eclipse user.i've been developing a java swt application but it shows me error whenever i try to import

import org.eclipse.jface.viewers.CheckboxTableViewer;
import org.eclipse.jface.viewers.ComboViewer;


I've checked in eclipse plugin,i do have jface plugin in there.so y does it shows error such as "cannot be resolved"?i'm using eclipse 3.2