(I thought I once read something about this in a book, but now I'm not sure where to find it. If this question reminds you of some material that you've read, please post a reference!)

What are the pros and the cons of primitives in interfaces?

In other words, is one of these preferable to the other and why? Perhaps one is preferable to the other in certain contexts?

public interface Foo {
    int getBar();
}

or

public interface Foo {
    Integer getBar();
}

Similarly:

public interface Boz {
    void someOperation(int parameter);
}

or

public interface Boz {
    void someOperation(Integer parameter);
}

Obviously there's the issue of having to deal with nulls in the non-primitive case, but are there deeper concerns?