Java Reference
In-Depth Information
Local Classes
A
local class
isaclassthatisdeclaredanywherethatalocalvariableisdeclared.Fur-
thermore,ithasthesamescopeasalocalvariable.Unlikeananonymousclass,alocal
class has a name and can be reused. Like anonymous classes, local classes only have
enclosing instances when used in nonstatic contexts.
A local class instance can access the surrounding scope's local variables and para-
meters.However,thelocalvariablesandparametersthatareaccessedmustbedeclared
final
. For example,
Listing 3-12
'
s local class declaration accesses a final parameter
and a final local variable.
Listing 3-12.
Declaring a local class
class EnclosingClass
{
void m(final int x)
{
final int y = x*2;
class LocalClass
{
int a = x;
int b = y;
}
LocalClass lc = new LocalClass();
System.out.println(lc.a);
System.out.println(lc.b);
}
}
local class named
LocalClass
. This local class declares a pair of instance fields (
a
and
b
)thatareinitializedtothevaluesof
final
parameter
x
and
final
localvariable
y
when
LocalClass
isinstantiated:
new EnclosingClass().m(10);
,forex-
ample.
Listing 3-13
demonstrates this local class.
Listing 3-13.
Demonstrating a local class
