Java Reference
In-Depth Information
Figure 21.4. A
Machine
object can create an appropriate
MachinePlanner
instance for
itself.
Suppose that you notice that subclasses of
Machine
include similar techniques for lazy-
initializing a planner. The
ShellAssembler
class has a
ShellPlanner
attribute that it
calls
planner
and that
ShellAssembler
initializes in its
getPlanner()
method:
public MachinePlanner getPlanner()
{
if (planner == null)
{
planner = new ShellPlanner(this);
}
return planner;
}
The
StarPress
class also has a
planner
attribute but declares it to be of type
StarPressPlanner
. The
getPlanner()
method of
StarPress
also lazy-initializes the
planner
attribute:
public MachinePlanner getPlanner()
{
if (planner == null)
{
planner = new StarPressPlanner(this);
}
return planner;
}
The other subclasses of
Machine
have similar approaches to creating a planner only when it
is first needed.
