¥Assume that we want to design the data for an online city phone
book. In contrast to our DeptDirectory example,
such a directory will contain several different
kinds of listings: businesses, residences, and
government agencies.
¥The entry data for such a directory is represented by using the union pattern
to identify the common behavior among the various
kinds of listings.
¥In this case, the common behavior is the existence of a String name for the listing and the String text of the listing (given by toString()).