Java Reference
In-Depth Information
super.describe();
}
The modified
Car
class now has two
describe()
methods, the preceding ex-
plicitly declared method and the method inherited from
Vehicle
. The
void de-
scribe(String owner)
method does not override
Vehicle
's
describe()
method. Instead, it overloads this method.
TheJavacompilerhelpsyoudetectanattempttooverloadinsteadofoverrideameth-
odatcompiletimebylettingyouprefixasubclass'smethodheaderwiththe
@Over-
ride
annotation, as shown below—I discuss annotations in
Chapter 3
:
@Override
void describe()
{
System.out.print("This car is a ");
super.describe();
}
Specifying
@Override
tellsthecompilerthatthemethodoverridesanothermethod.
Ifyouoverloadthemethodinstead,thecompilerreportsanerror.Withoutthisannota-
tion,thecompilerwouldnotreportanerrorbecausemethodoverloadingisavalidfea-
ture.
Tip
Get into the habit of prefixing overriding methods with the
@Override
an-
notation. This habit will help you detect overloading mistakes much sooner.
I previously presented the initialization order of classes and objects, where you
learnedthatclassmembersarealwaysinitializedfirst,andinatop-downorder(thesame
orderappliestoinstancemembers).Implementationinheritanceaddsacouplemorede-
tails:
• Asuperclass'sclassinitializersalwaysexecutebeforeasubclass'sclassinitial-
izers.
• Asubclass'sconstructoralwayscallsthesuperclassconstructortoinitializean
object's superclass layer before initializing the subclass layer.
Java's support for implementation inheritance only permits you to extend a single
class. You cannot extend multiple classes because doing so can lead to problems. For
example,supposeJavasupportedmultipleimplementationinheritance,andyoudecided
tomodela
flying horse
(fromGreekmythology)viatheclassstructureshownin
Listing
