Java Reference
In-Depth Information
class can also access the private members of the inner class, but only
by an explicit reference to an inner class object such as
lastAct
. While
an object of the inner class is always associated with an object of the
enclosing class, the converse is not true. An object of the enclosing class
need not have any inner class objects associated with it, or it could have
many.
When
deposit
creates an
Action
object, a reference to the enclosing
BankAccount
object is automatically stored in the new
Action
object. Using
this saved reference, the
Action
object can always refer to the enclos-
ing
BankAccount
object's
number
field by the simple name
number
, as shown
in
toString
. The name of the reference to the enclosing object is
this
preceded by the enclosing class namea form known as
qualified-
this
.
For example,
toString
could reference the
number
field of the enclosing
BankAccount
object explicitly:
return BankAccount.this.number + ": " + act + " " + amount;
The qualified-
this
reference reinforces the idea that the enclosing object
and the inner object are tightly bound as part of the same implement-
ation of the enclosing class. This is further reinforced by the
quali-
fied-
super
reference, which allows access to members of the enclosing
instance's superclass that have been hidden, or overridden, by the en-
closing class. For example, given a class
T
that extends
S
, within
T
we
can invoke the superclass implementation of a method
m
, by using
su-
per.m()
in an expression. Similarly, in an inner class of
T
, we can invoke
the same implementation of
m
using
T.super.m()
in an expressiona quali-
fied-
super
referenceand similarly for fields of
S
hidden by fields in
T
.
A nested class can have its own nested classes and interfaces. Referen-
ces to enclosing objects can be obtained for any level of nesting in the
same way: the name of the class and
this
. If class
X
encloses class
Y
which encloses class
Z
, code in
Z
can explicitly access fields of
X
by using
X.this
.
