Object-Oriented Design - Java Software Solutions: Foundations of Program Design - page 320

LISTING 7.7 continued

private String streetAddress, city, state;
private long zipCode;

//-----------------------------------------------------------------
// Constructor: Sets up this address with the specified data.
//-----------------------------------------------------------------
public Address (String street, String town, String st, long zip)
{
streetAddress = street;
city = town;
state = st;
zipCode = zip;
}

//-----------------------------------------------------------------
// Returns a description of this Address object.
//-----------------------------------------------------------------
public String toString()
{
String result;

result = streetAddress + "\n";
result += city + ", " + state + " " + zipCode;

return result;
}
}

The more complex an object, the more likely it will need to be represented as
an aggregate object. In UML, aggregation is represented by a connection between
two classes, with an open diamond at the end near the class that is the aggregate.
Figure 7.2 shows a UML class diagram for the StudentBody program.
Note that in previous UML diagram examples and in Figure 7.2, strings are not
represented as separate classes with aggregation relationships, though technically
they could be. Strings are so fundamental to programming that often they are
represented as though they were a primitive type in a UML diagram.

The this Reference
Before we leave the topic of relationships among classes, we should examine
another special reference used in Java programs called the this reference. The
word this is a reserved word in Java. It allows an object to refer to itself. As we
have discussed, a nonstatic method is invoked through (or by) a particular object