Query regarding generic sObject and specific sObject

Question

I was going through the 'Apex and Database basics' module in Trailhead and came across the following sentence in one of the units:

This example shows how the generic sObject variable can be assigned to any Salesforce object: an account and a custom object called Book__c.

sObject sobj1 = new Account(Name='Trailhead');
sObject sobj2 = new Book__c(Name='Workbook 1');

I think the sentence should have been like this: This example shows how the generic sObject variable can be assigned any Salesforce object: an account and a custom object called Book__c. What I mean is isnt the specific object being assigned to the generic object and not the other way around? I hope I've clarified my concern.

Answer 1

Yes, you are correct. The specific type is indeed being assigned to the generic type. The way the trailhead module words it is indeed backwards (i.e. it describes Account acct = genericSObject;)

The action of going from a more specific type to a more general one is called up-casting. It's (almost) always possible to perform an up-cast (there are a few specific scenarios where it isn't possible, but those are the exception rather than the rule).

It is, however, also possible to down-cast in certain scenarios. As an example, try running the following code in an anonymous apex window:

Account myAccount = new Account(Name = 'my new account');
SObject genericSObj = myAccount;
Account otherAccountVariable = (Account)genericSObj;

Even though we stored the Account as a more general SObject type, Salesforce is able to remember enough about the original object in this scenario that we can down-cast back to an Account.

The (Account) part of (Account)genericSObj; is an example of explicitly type-casting an expression (whereas genericSObj = myAccount; is implicitly doing a type-cast). We need to explicitly type-cast when trying to down-cast.

Answer 2

It's just the way you are reading it, I think in English that's a correct way of saying: "You can assign an Account type to the generic sObject type". You're understanding is correct.