public String getIdentifier() returns the unique identifier
      of this activity.
    Parameters
None
Returns
Returns a string that represents the ID.
Example
    ActivityStreamService activityStreamService = session.getServiceRegistry()
            .getActivitystreamService();
    try {
        // Get all entries
        List<ActivityEntry> entries = activityStreamService.getActivityStream();
        for (ActivityEntry entry : entries) {
            Log.d(TAG, "ActivityEntry:");
            Log.d(TAG, "createdBy: " + entry.getcreatedBy());
            Log.d(TAG, "creationTime: " + entry.getCreationTime().getTime().toString());
            Log.d(TAG, "identifier: " + entry.getIdentifier());
            Log.d(TAG, "siteShortName: " + entry.getSiteShortName());
            Log.d(TAG, "type: " + entry.getType());
            Log.d(TAG, "----------");
        }
    } // end try
    catch (AlfrescoServiceException e){
        Log.d(TAG, "Exception:" + e.toString());
        return 1;
    }
        
      Would result in output such as: