Passing string of sobject name via trigger on ...how to fetch the sobject name of type sobject in class..

```
class
{
method(String operationType,list <Sobject> ,list<sobject>,string objecttype)
{
  //operation type means insert or update or delete
//objecttype means 'customobj__c'
Sobject obj;
}
}

```

I want to utilise objecttype to get sobject in obj

Or any help in getting the sobject?