import org.eclipse.jface.action.ActionContributionItem;
import org.eclipse.jface.action.IAction;
import org.eclipse.jface.action.IContributionManagerOverrides;

public class GeometryEditorActionContributionItem extends
		ActionContributionItem {

	public GeometryEditorActionContributionItem(IAction action) {
		super(action);
	}

	public void update(String propertyName) {
		final IAction action = getAction();
		if (getWidget() != null) {
			boolean enableStateChanged = propertyName == null
					|| propertyName.equals(IAction.ENABLED)
					|| propertyName.equals(IContributionManagerOverrides.P_ENABLED);
			if (enableStateChanged) {				
				if (action.isEnabled() && !isEnabledAllowed()) {
					return;
				}
			}
		}
		super.update(propertyName);
	}	
}

    private final void add(IToolBarManager toolBarManager, IAction action) {
	GeometryEditorActionContributionItem item = new GeometryEditorActionContributionItem(action);
        toolBarManager.add(item);
    }
	
    public void contributeToToolBar(IToolBarManager toolBarManager) {
        super.contributeToToolBar(toolBarManager);
        
        add(toolBarManager, zoomInAction);
        add(toolBarManager, zoomOutAction);
        ...
    }