Java Reference
In-Depth Information
Anchoring a Chain
When you write the
getResponsible()
method for
MachineComponent
, you have to
consider that a
MachineComponent
object's parent might be null. Alternatively, you can
tighten up your object model, insisting that
MachineComponent
objects have a non-null
parent. To achieve this, add a parent argument to the constructor for
MachineComponent
.
(You may want to throw an exception if the supplied object is null.) Also consider that an
object will be the
root
—a distinguished object that has no parent. A reasonable approach is to
create a
MachineRoot
class as a subclass of
MachineComposite
(not
MachineComponent
). Then you can guarantee that a
MachineComponent
object always
has a responsible engineer if
•
The constructor(s) for
MachineRoot
require an
Engineer
object
•
The constructor(s) for
MachineComponent
require a non-null parent object that is
itself a
MachineComponent
