I've noticed in some of the example code that reference types are used instead of primitives. For example, for an auto-increment id value like the following.

private Integer id;

public Integer getId() {
return id;
}

instead of,

private int id;

public int getId() {
return id;
}

I'm wondering if there are any advantages/disadvantages to using reference types instead of primitive types? I'm guessing that the main advantage is that you can easily distinguish whether the property has a null value in the database.

I'm wondering if I should just use reference types for everything? Does anyone have any recommendations?

I usually use the reference type since null is a natural value for unsaved entities.

But it happens that you are very concerned about your entity memory footprint and thus use a primitive type.

Actually it's up to you if your can find a defaut value for unsaved-value in you business case.