Java Reference
In-Depth Information
An implementation of the Java programming language must ensure, as part of linkage, that
the method
m
still exists in the type
T
. If this is not true, then a
NoSuchMethodError
(which is
a subclass of
IncompatibleClassChangeError
) occurs.
If the invocation mode is
interface
, then the implementation must also check that the target
reference type still implements the specified interface. If the target reference type does not
still implement the interface, then an
IncompatibleClassChangeError
occurs.
The implementation must also ensure, during linkage, that the type
T
and the method
m
are
accessible:
• For the type
T
:
♦ If
T
is in the same package as
C
, then
T
is accessible.
♦ If
T
is in a different package than
C
, and
T
is
public
, then
T
is accessible.
♦ If
T
is in a different package than
C
, and
T
is
protected
, then
T
is accessible if
and only if
C
is a subclass of
T
.
• For the method
m
:
♦ If
m
is
protected
, then
m
is accessible if and only if either
T
is in the same pack-
age as
C
, or
C
is
T
or a subclass of
T
.
♦ If
m
has default (package) access, then
m
is accessible if and only if
T
is in the
same package as
C
.
♦ If
m
is
private
, then
m
is accessible if and only if
C
is
T
, or
C
encloses
T
, or
T
encloses
C
, or
T
and
C
are both enclosed by a third class.
15.12.4.4. Locate Method to Invoke
The strategy for method lookup depends on the invocation mode.
If the invocation mode is
static
, no target reference is needed and overriding is not allowed.
Method
m
of class
T
is the one to be invoked.
Otherwise, an instance method is to be invoked and there is a target reference. If the target
reference is
null
, a
NullPointerException
is thrown at this point. Otherwise, the target reference
is said to refer to a
target object
and will be used as the value of the keyword
this
in the
invoked method. The other four possibilities for the invocation mode are then considered.
