public ContributionComparator getComparatorFor(String contributionType) {
	if (contributionType.equals(IContributionService.TYPE_PREFERENCE)) {
		return new PreferencesComparator();
	}
	else {
		return super.getComparatorFor(contributionType);
	}
}

public class PreferencesComparator extends ContributionComparator {

	public int category(IComparableContribution c) {
		if (c instanceof WorkbenchPreferenceNode) {
			String id = ((WorkbenchPreferenceNode) c).getId();
			if (PlanTransportTourPreferencePage.ID.equals(id)) {
				return 1;
			}
			else if (PlanTransportSequencePreferencePage.ID.equals(id)) {
				return 2;
			}
			else if (PlanTransportPositionPreferencePage.ID.equals(id)) {
				return 3;
			}
			else {
				return super.category(c);
			}
		}
		else {
			return super.category(c);
		}
	}
}