pushing the JLS envelope... (6.4.2. Obscuring)

[Andreas Leitgeb]

Ok, I know that this breaks conventions and common sense, but
just for the sake of understanding the JLS...

--- snip foo/Foo.java ---
package foo;
public class Foo {
public static String bad_name = "boo!"; // bad name for a field
public static class bad_name { // even worse, because lower case
public static void foo() { }
}
static {
bad_name.foo(); // doesn't work, because field obscures type - Ok.
foo.Foo.bad_name.foo(); // fqn doesn't work, either, but shouldn't it?
}
}
--- end snip ---

JLS (6.4.2. Obscuring) has to say about this case:
- If a field name obscures a type name, then a
fully qualified name for the type can be used
unless the type name denotes a local class (§14.3).
("bad_name" isn't a local class, so the "unless"-part doesn't apply.)

Even if the field was non-static, the compiler still doesn't use
the type but rather complains about unavailability of the field,
even with the fqn.

PS: suggesting "rename the field or (better) the type" as a solution
is really missing the point of this post.

 

[Daniele Futtorovic]

Ok, I know that this breaks conventions and common sense, but
just for the sake of understanding the JLS...

--- snip foo/Foo.java ---
package foo;
public class Foo {
public static String bad_name = "boo!"; // bad name for a field
public static class bad_name { // even worse, because lower case
public static void foo() { }
}
static {
bad_name.foo(); // doesn't work, because field obscures type - Ok.
foo.Foo.bad_name.foo(); // fqn doesn't work, either, but shouldn't it?
}
}
--- end snip ---

JLS (6.4.2. Obscuring) has to say about this case:
- If a field name obscures a type name, then a
fully qualified name for the type can be used
unless the type name denotes a local class (§14.3).
("bad_name" isn't a local class, so the "unless"-part doesn't apply.)

Even if the field was non-static, the compiler still doesn't use
the type but rather complains about unavailability of the field,
even with the fqn.

PS: suggesting "rename the field or (better) the type" as a solution
is really missing the point of this post.

The FQN is ambiguous. According to [6.5.2. Reclassification of
Contextually Ambiguous Names]:If the name to the left of the "." is reclassified as a TypeName, then:

If the Identifier is the name of a method or field of the type
denoted by TypeName, this AmbiguousName is reclassified as an
ExpressionName.

*Otherwise*, if the Identifier is the name of a member type of the
type denoted by TypeName, this AmbiguousName is reclassified as a TypeName.
<<<<<<

Ergo, foo.Foo.bad_name refers to foo's the member of type String,
bad_name (great name btw.).



.... At least that's how I'd interpret it.

 

[Lew]

Great question.

The FQN is ambiguous. According to [6.5.2. Reclassification of

Great answer.

Contextually Ambiguous Names]:If the name to the left of the "." is reclassified as a TypeName, then:

If the Identifier is the name of a method or field of the type
denoted by TypeName, this AmbiguousName is reclassified as an
ExpressionName.

*Otherwise*, if the Identifier is the name of a member type of the
type denoted by TypeName, this AmbiguousName is reclassified as a TypeName.
<<<<<<

Ergo, foo.Foo.bad_name refers to foo's the member of type String,
bad_name (great name btw.).

"bad_name" == great name.

... At least that's how I'd interpret it.

Makes sense to me, both question and answer.

I shall rethink it a couple or few more times, but so far you seem to have it aright.
If so, then

foo.Foo.bad_name.foo(); // fqn doesn't work, either, but shouldn't it?

would fail to compile because 'String' doesn't have a method 'foo()'.

 

[Andreas Leitgeb]

My fault for stopping reading at (6.4.2) in the JLS...

It seems that "Obscuring" is really only meant between some
visible field and some visible type which however stem from
different qualifying paths (or local versus qualifyable).

The FQN is ambiguous. According to [6.5.2. Reclassification of
Contextually Ambiguous Names]:

Thanks for pointing that out (although I had to read all the
6.5 and 6.5.1 to make any sense of the quoted part of 6.5.2 !

After having determined "foo.Foo" as a Type and considering
Identifier "bad_name":

If the Identifier is the name of a method or field of the type
denoted by TypeName, this AmbiguousName is reclassified as an
ExpressionName.

*Otherwise*, if the Identifier is the name of a member type of the
type denoted by TypeName, this AmbiguousName is reclassified as a TypeName.

So, this is, where field "bad_name" wins over type "bad_name" and
that is regardless that the next identifier is not a member of that
field's type.

Now, I'm going to be (unsolicitedly) sadistic, maybe causing some cringe...
In my example, if I rewrote the static initializer block as follows:
static { bad_name bad_name = null; bad_name.foo(); }
then it becomes "correct" w.r.t. the JLS, because the name now first
appears in a context that infers a type name, then as a local variable
that beats the field ;-)

Thanks, Daniele, for pointing out, that "Obscuring" wasn't the case.

 

[Daniele Futtorovic]

My fault for stopping reading at (6.4.2) in the JLS...

It seems that "Obscuring" is really only meant between some
visible field and some visible type which however stem from
different qualifying paths (or local versus qualifyable).

The FQN is ambiguous. According to [6.5.2. Reclassification of
Contextually Ambiguous Names]:

Thanks for pointing that out (although I had to read all the
6.5 and 6.5.1 to make any sense of the quoted part of 6.5.2 !

After having determined "foo.Foo" as a Type and considering
Identifier "bad_name":

If the Identifier is the name of a method or field of the type
denoted by TypeName, this AmbiguousName is reclassified as an
ExpressionName.

*Otherwise*, if the Identifier is the name of a member type of the
type denoted by TypeName, this AmbiguousName is reclassified as a TypeName.

So, this is, where field "bad_name" wins over type "bad_name" and
that is regardless that the next identifier is not a member of that
field's type.

Now, I'm going to be (unsolicitedly) sadistic, maybe causing some cringe...
In my example, if I rewrote the static initializer block as follows:
static { bad_name bad_name = null; bad_name.foo(); }
then it becomes "correct" w.r.t. the JLS, because the name now first
appears in a context that infers a type name, then as a local variable
that beats the field ;-)

You're such a dirty man, you know that? ;P

Thanks, Daniele, for pointing out, that "Obscuring" wasn't the case.

Thank you for giving me the opportunity to find out what was happening
there.