Design Patterns Java™ Workbook

Appendix C. UML at a Glance

Figure C.2. A MachineComposite object contains either Machine objects or other
composites. The Customer class depends on the LikeMyStuff class without
instantiating it.

• Show a class name or a method name in italics to indicate that the class or method is
  abstract.


• Use a closed, hollow arrowhead to point to a class's superclass.


• Use a line between classes to indicate that instances of the classes are connected. Most
  commonly, a line on a class diagram means that one class has an instance variable that
  refers to the other class. The classes MachineComposite class, for example, uses a
  List variable that contains references to other machine components.


• Use a diamond to show that instances of a class contain a collection of instances of
  another class.


• An open arrowhead indicates navigability. Use it to emphasize that one class has a
  reference to another and that the pointed-to class does not have a back reference.


• A multiplicity indicator, such as 0..1, indicates how many connections may appear
  between objects. Use an asterisk (*) to indicate that zero or more instances of an
  object of a class may be connected to objects of an associated class.


• To show that a method may throw an exception, use a dashed arrow pointing from the
  method to the exception class. Label the arrow with a «throws» stereotype.