Bug 261506 [CommonNavigator] NavigatorDNDService seems like it can use only interfaces
The NavigatorDNDService class seems like it could use only interface APIs and function properly. Patch attached.
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/dnd/NavigatorDnDService.java
CommonDropAdapterDescriptor[] descriptors, IStructuredSelection aSelection) {
		Set assistants = new LinkedHashSet(); 
			
		for (int i = 0; i < descriptors.length; i++) {
			if(descriptors[i].areDragElementsSupported(aSelection)) {
				assistants.add(getAssistant(descriptors[i]));
			}
		}  
		return (CommonDropAdapterAssistant[]) assistants
				.toArray(new CommonDropAdapterAssistant[assistants.size()]);
	}
	private CommonDropAdapterAssistant getAssistant(
			CommonDropAdapterDescriptor descriptor) {
		CommonDropAdapterAssistant asst = (CommonDropAdapterAssistant) dropAssistants
				.get(descriptor);
		if (asst != null) {
			return asst;
		}
		synchronized (dropAssistants) {
			asst = (CommonDropAdapterAssistant) dropAssistants.get(descriptor);
			if (asst == null) {
				dropAssistants.put(descriptor, (asst = descriptor
						.createDropAssistant()));
				asst.init(contentService);
			}
		}
		return asst;
	}
}