Programming :: Ways Of Handling The ADT Interface?

During my read, "Code Complete",the author described the different ways of handling the ADT interface.He has wrote this passage:

Quote:

Option 2: Explicitly provide the data used by the ADT services. In this approach, you declare the data that the ADT uses within each routine that uses an ADT service. In other words, you create a Font data type that you pass to each of the ADT service routines. You must design the ADT service routines so that they use the Font data that's passed to them each time they're called. The client code doesn't need a font ID if you use this approach because it keeps track of the font data itself. (Even though the data is available directly from the Font data type, you should access it only with the ADT service routines.This is called keeping the structure "closed.") The advantage of this approach is that the ADT service routines don't have to look up font information based on a font ID. The disadvantage is that it exposes font data to the rest of the program, which increases the likelihood that client code will make use of the
ADT's implementation details that should have remained hidden within the ADT.

The problem is that it is a bit subtle in terms of coding for me. Can anybody give more concrete example, in working codes, especially in Java?