Is it a good practice to use Optional as an attribute in a class?

Question

I have read something about the purpose of Optional (unfortunately I don't remember where) in Java 8, and I was surprised the writer didn't mention the use of an Optional as an attribute in a class.

Since I am using optionals pretty frequently in my classes, I was wondering if this is a good practice. Or could I better just use normal attributes, which return null when they are not set?

Note: It may look like my question is opinion based, but I get the feeling using Optional in a class is really not the way to go (after reading the mentioned post). However, I like to use it and can't find any downside of using it.

Example

I would like to give an example to clarify. I have a class Transaction, which is built like this:

public class Transaction {

     private Optional<Customer> = Optional.empty();
     ....

vs

public class Transaction {

     private Customer = null;
     ....

When checking on a Customer, I think it is most logical to use transaction.getCustomer().isPresent() than transaction.getCustomer() != null. In my opinion the first code is cleaner than the second one.

Answer 1

Java 8's Optional was mainly intended for return values from methods, and not for properties of Java classes, as described in Optional in Java SE 8:

Of course, people will do what they want. But we did have a clear intention when adding this feature, and it was not to be a general purpose Maybe or Some type, as much as many people would have liked us to do so. Our intention was to provide a limited mechanism for library method return types where there needed to be a clear way to represent "no result", and using null for such was overwhelmingly likely to cause errors.

The key here is the focus on use as a return type. The class is definitively not intended for use as a property of a Java Bean. Witness to this is that Optional does not implement Serializable, which is generally necessary for widespread use as a property of an object.