using getAdministrativeResourceResolver(null) in AEM 6

I am trying to use the following line of code from http://helpx.adobe.com/experience-manager/using/using-sling-apis.html

ResourceResolver resourceResolver =resolverFactory.getAdministrativeResourceResolver(null); //line 82

but I get java.lang.NullPointerException
    at shoprite.holdings.impl.FetchStores.jcrStoresUptodate(FetchStores.java:82)

    at shoprite.holdings.impl.FetchStores.<init>(FetchStores.java:66)

    at shoprite.holdings.impl.StoreLocatorImpl.getStores(StoreLocatorImpl.java:26)

    at shoprite.holdings.TestGetStores.main(TestGetStores.java:14)

I have tried to replace this with the following code from the blog "AEM6: ResourceResolver access in services" http://cqblog.inside-solutions.ch/category/cq5/.

Map<String, Object> param = new HashMap<String, Object>();
        param.put(ResourceResolverFactory.SUBSERVICE, "readService");
        ResourceResolver resolver = null;
        try {
            resolver = resolverFactory.getServiceResourceResolver(param);

However I get the following errors

The method getServiceResourceResolver(Map<String,Object>) is undefined for the type ResourceResolverFactory

and 

SUBSERVICE cannot be resolved or is not a field.

From this I am assuming that the version of ResourceResolver I am using is not concurrent. I am definitely on version 6 of AEM. I am also not sure why the code example from AEM 5.6 ResourceResolver resourceResolver =resolverFactory.getAdministrativeResourceResolver(null); gives me a NullPointerException