Java Reference
In-Depth Information
SOLUTION 26.2
The call to
notify()
in the
pop()
method will wake up a thread that was waiting for
the stack to make some room. The awakened thread must then wait to obtain the monitor.
Because the
pop()
method is
synchronized
, it holds the monitor until the method
completes.
SOLUTION 26.3
The problems in the model are as follows.
•
The
Rocket
class can't extend two classes.
•
The
Rocket.clone()
method can't have the same signature as and a different
return type from the method it overrides.
•
The
Rocket.clone()
method can't reduce visibility from
protected
to
private
.
•
The
Rocket.clone()
method can't throw an extra exception. You could cure this
problem
if
you
made
RocketCloneException
an
extension
of
CloneNotSupportedException
.
SOLUTION 26.4
Questionable aspects of the model follow.
•
The
FireworkCollection
class is useful as a collection that contains only
a certain type of object. However, such a collection is either a list or a set, and it
should be named accordingly.
•
The
FireworkCollection
class stores
Firework
objects in a set instead of a list.
This makes it difficult to imagine what a call to, say,
get(0)
will return.
•
The
FireworkCollection
class has an
iterator()
function, which is good, but
it returns
Iterator
, which is questionable. The returned iterator will have a
next()
method that returns an
Object
that the caller will have to cast to
Firework
. This
defeats the idea of having a separate collection class for fireworks.
•
The fireworks hierarchy comprehends the fact that a firework's type does not always
indicate whether the firework will explode.
For example, rockets may or may not explode, although firecrackers always explode
and sparklers never do. The
setExplodes()
method allows flexibility in modeling
firework types but also allows setting a
Sparkler
object to be an exploding type of
firework. You should avoid this type of modeling error. In this case, it might work to
create an
ExplodingFirework
subclass of
Firework
.
•
The
setExplodes()
method of
Firecracker
throws
an
IllegalArgumentException
if the argument is false, as all firecrackers
explode. It is inconsistent to have this method throw an exception without extending
this thought to
Sparkler
, whose instances should never explode.
