Bug 31683 Show In doesn't work for class file in rt.jar
I20030611 - create Test project that uses Jar container - open NumberFormat.class - activate Show In... and choose Package Explorer Observe: NumberFormat.class doesn't get revealed.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/packageview/PackageExplorerPart.java
private Object filter(Object object, Object parent, ViewerFilter[] filters) {
				for (int i = 0; i < filters.length; i++) {
					ViewerFilter filter = filters[i];
					if (!filter.select(fViewer, parent, object))
						return null;
				}
				return object;
			}
		
			/* Checks if a filtered object in essential (ie. is a parent that
			 * should not be removed).
			 */ 
			private boolean isEssential(Object object) {
				try {
					if (!isFlatLayout() && object instanceof IPackageFragment) {
						IPackageFragment fragment = (IPackageFragment) object;
						return !fragment.isDefaultPackage() && fragment.hasSubpackages();
					}
				} catch (JavaModelException e) {
					JavaPlugin.log(e);
				}
				return false;
			}
			
			protected void handleInvalidSelection(ISelection invalidSelection, ISelection newSelection) {
				IStructuredSelection is= (IStructuredSelection)invalidSelection;
				List ns= null;
				if (newSelection instanceof IStructuredSelection) {
					ns= new ArrayList(((IStructuredSelection)newSelection).toList());