Design Patterns Java™ Workbook

Composite (Chapter 5)

SOLUTION 5.1

One answer is that Design Patterns (Gamma et al. 1995) shows Component as an abstract class, so Java developers may implement it that way without considering the use of a Java interface. Another answer is that the Component superclass often has fields and methods that its subclasses can share. For example, the Component class may have a name instance variable and a concrete toString() method that uses it.

SOLUTION 5.2

For the Machine class, getMachineCount() should be something like: public int getMachineCount() { return 1; } The class diagram shows that MachineComposite uses a List object to track its components. To count the machines in a composite, you might write: public int getMachineCount() { int count ...