Solutions - Design Patterns Java - page 291

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;
}