Is it better to pass reference to an object or pass individual attributes in an object in Java?

Question

I'm dealing with legacy code and I constantly see method calls with multiple attributes from the same object being passed into a method:

update(user.getID(), user.getLanguage() etc...)

Is there a distinct advantage or disadvantage to doing it this way or would I just be as well to pass in the user object (in this case) and deal with attributes within the method called?

Follow Up:

Lots of excellent answers, thank you. Apologies for the lack of exact detail in the question but as I said this is seen all over the system I am working on and this seemed like a nice simple example. Please feel free to turn this question into a community wiki question as no one answer can possibly be accepted over others as they're all good and have valid points.

Answer 1

Both have their advantages. I'd decide for each method depending on what it is supposed to do. For legacy code, though, I'd prefer to not change anything unless there is actually a problem.

Pro several values, con object reference:

• you're not bound to a specific class, you can pass values from other sources
• method cannot (unexpectedly) change object state (C++ could use "const" for this)

Pro passing a single user object:

• you're bound to user objects, making it difficult to accidentally pass unrelated / invalid values
• it's obvious that the method expects data of a user object
• changing (e.g. renaming) a getter requires changes at all invocations of the method and not just in its implementation
• similar if a new property is added and needs to be passed
• method can change object state

As you see a property can be considered an advantage or disadvantage depending on your needs.

Answer 2

In fact, it would be much, much better to pass a reference to the object, for two reasons:

• it avoids repetition of all the getters in every place the method is called (DRY principle)
• it leads to shorter method signatures. Methods should almost never have more than three parameters because it's too easy to get confused about the order, and hard to refactor.

To avoid excessively long parameter lists, the recommended refactoring is to create a object that contains all the data - aren't you lucky that you already have such an object?