this.initialized = true;

this.firstxpcom = Components.classes["@senecac.on.ca/firstxpcom;1"]

this.firstxpcom.name = "First XPCOM";

// Use the Alerts Service to display the results to the user.

var alertsService = Components.classes["@mozilla.org/alerts-service;1"]

alertsService.showAlertNotification(null, this.firstxpcom.name, this.total,

false, "", null);

this.firstxpcom = Components.classes["@senecac.on.ca/firstxpcom;1"]

var alertsService = Components.classes["@mozilla.org/alerts-service;1"]

In the former case we use '''createInstance''', which gives us a new unique instance. In the latter, we use '''getService''', which returns a shared instance of an existing component (i.e., a Singleton). Unlike IFirstXpcom, which can be created many times by different callers, the nsIAlertsService is a shared component, because only one pop-up message at a time can be shown to the user.