A.2 Class Relationships

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	Building Parsers with Java By Steven  John  Metsker
	Table of Contents
	Appendix  A.   UML Twice Distilled

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Figure A.2 shows a few of the UML's features for modeling class relationships.

Figure A.2. Class relations. Various lines between classes indicate relationships between objects of the classes.

In Figure A.2, note the following.

• A diagram may show a class name or method name in italics to indicate that the class or method is abstract.

• A large, open arrowhead points to a class's superclass.

• A line between classes indicates that instances of the classes are connected in some way. Most commonly, a line on a class diagram means that one class has an instance variable that refers to the other class. The classes Alternation and Sequence , for example, use a Vector variable that CollectionParser declares to hold collections of other parsers.

• An asterisk ( * ) indicates that zero or more instances of an object of a class may be connected to objects of an associated class. For example, a Sequence object has a reference to zero or more Parser objects.

• A multiplicity indicator, such as 0..1 , indicates how many connections may appear between objects. For example, a Parser object can have zero or one associated Assembler objects.

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