Java Reference
In-Depth Information
•
V
is [un]assigned before any other statement
S
of the block iff
V
is [un]assigned
after the statement immediately preceding
S
in the block.
We say that
V
is definitely unassigned everywhere in a block
B
iff:
•
V
is definitely unassigned before
B
.
•
V
is definitely assigned after
e
in every assignment expression
V
=
e
,
V
+=
e
,
V
-=
e
,
V
*=
e
,
V
/=
e
,
V
%=
e
,
V
<<=
e
,
V
>>=
e
,
V
>>>=
e
,
V
&=
e
,
V
|=
e
, or
V
^=
e
that oc-
curs in
B
.
•
V
is definitely assigned before every expression
++
V
,
--
V
,
V
++
, or
V
--
. that occurs in
B
.
These conditions are counterintuitive and require some explanation. Consider
a simple assignment
V
=
e
. If
V
is definitely assigned after
e
, then either:
• The assignment occurs in dead code, and
V
is vacuously definitely as-
signed. In this case, the assignment will not actually take place, and
we can assume that
V
is not being assigned by the assignment expres-
sion. Or:
•
V
was already assigned by an earlier expression prior to
e
. In this case
the current assignment will cause a compile-time error.
So, we can conclude that if the conditions are met by a program that causes no
compile time error, then any assignments to
V
in
B
will not actually take place
at run time.
16.2.3. Local Class Declaration Statements
•
V
is [un]assigned after a local class declaration statement (§
14.3
) iff
V
is
[un]assigned before the local class declaration statement.
16.2.4. Local Variable Declaration Statements
no variable initializers iff
V
is [un]assigned before the local variable declaration
statement.
•
V
is definitely assigned after a local variable declaration statement that contains at
least one variable initializer iff either
V
is definitely assigned after the last variable
initializer in the local variable declaration statement or the last variable initializer
in the declaration is in the declarator that declares
V
.
•
V
is definitely unassigned after a local variable declaration statement that contains
at least one variable initializer iff
V
is definitely unassigned after the last variable
