Design Patterns Java™ Workbook

Appendix B. Solutions

SOLUTION 5.4.......................................................................................................................................

The program prints out the number 4.

Only three machines are in the plant factory, but machine m is counted by both plant and
bay. Both of these objects contain lists of machine components that refer to machine m.

The results could be worse. If, say, an engineer adds the plant object as a component of the
bay composite, a call to getMachineCount() will enter an infinite loop.

SOLUTION 5.5.......................................................................................................................................

A reasonable implementation of MachineComposite.isTree() is:

protected boolean isTree(Set visited)
{
visited.add(this);
Iterator i = components.iterator();
while (i.hasNext())
{
MachineComponent c = (MachineComponent) i.next();
if (visited.contains(c) || !c.isTree(visited))
{
return false;
}
}
return true;
}