How would I rewrite this to satisfy the code checker?

[laredotornado]

Hi,
I'm using Java 1.5, Eclipse Galileo on Mac 10.5.6 and the code
checking plug-in (PMD) is complaining about the below block ...

BufferedReader reader = new BufferedReader(new InputStreamReader
(fileStream));
StringBuilder stringBuf = new StringBuilder();
String line = null;
...
while ((line = reader.readLine()) != null) {
stringBuf.append(line + "\n");
}

saying, "Avoid assignments in operands". How would I rewrite the
while loop to make this error go away but achieve the same
functionality?

Thanks, - Dave

 

[Lew]

I'm using Java 1.5, Eclipse Galileo on Mac 10.5.6 and the code
checking plug-in (PMD) is complaining about the below block ...

                          BufferedReader reader = new BufferedReader(new InputStreamReader
(fileStream));

Hey, lighten up on the indentation!

Use a maximum of four spaces per indent level and don't use TAB
characters for Usenet code posts.

                          StringBuilder stringBuf = new StringBuilder();

Your variable name choice is slightly misleading.

                          String line = null;
                          ...
                                  while ((line = reader.readLine()) != null) {
                                          stringBuf.append(line + "\n");
                                  }

saying, "Avoid assignments in operands".  How would I rewrite the
while loop to make this error go away but achieve the same
functionality?

It's not an error, it's a warning and not even a standard warning for
Java. It's a perfectly legal construct. However, it does elevate the
scope of the variable 'line' beyond where it should be. Also, the
assignment of 'null' to it is superfluous. So really your "checker"
is giving you good advice.

You could use a 'for' loop.

for ( String line = reader.readLine(); line != null; line =
reader.readLine() )
{
...
}

Does FindBugs work on the Mac?

 

[laredotornado]

Hey, lighten up on the indentation!

Use a maximum of four spaces per indent level and don't use TAB
characters for Usenet code posts.


Your variable name choice is slightly misleading.



It's not an error, it's a warning and not even a standard warning for
Java.  It's a perfectly legal construct.  However, it does elevate the
scope of the variable 'line' beyond where it should be.  Also, the
assignment of 'null' to it is superfluous.  So really your "checker"
is giving you good advice.

You could use a 'for' loop.

 for ( String line = reader.readLine(); line != null; line =
reader.readLine() )
 {
   ...
 }

Does FindBugs work on the Mac?

Sweet! Works like a dream. 5 stars.

I don't know if FindBugs works on a Mac but there is a plug-in for
Eclipse and since Eclipse is cross-platform, I assume so, but haven't
tried FindBugs yet.

Thanks, -

 

[Arved Sandstrom]

On Nov 4, 2:21 pm, Lew <[email protected]> wrote:

[ SNIP ]

Sweet! Works like a dream. 5 stars.

I don't know if FindBugs works on a Mac but there is a plug-in for
Eclipse and since Eclipse is cross-platform, I assume so, but haven't
tried FindBugs yet.

Thanks, -

FindBugs Eclipse plugin and FindBugs standalone work just fine on Mac OS
X 10.5/10.6.

AHS

 

[Roedy Green]

hile ((line = reader.readLine()) != null) {
stringBuf.append(line + "\n");
}

saying, "Avoid assignments in operands". How would I rewrite the
while loop to make this error go away but achieve the same
functionality?

That code is fine. There is really no other way to do it. However in
general it is confusing to newbies if you write code of the form:

x = ( a = b ); // = assignment embedded in expression.
as opposed to
x = ( a == b );

 

[Tom McGlynn]

while ((line = reader.readLine()) != null) {
stringBuf.append(line + "\n");
} [code edited for appearance]
saying, "Avoid assignments in operands". How would I rewrite the
while loop to make this error go away but achieve the same
functionality?

That code is fine. There is really no other way to do it. However in
general it is confusing to newbies if you write code of the form:

x = ( a = b ); // = assignment embedded in expression.
as opposed to
x = ( a == b );

The problem with this idiom for me is that you have a choice of either
having a statement that has side effects, e.g., the original code, or
you need to duplicate the read statement. While both of these are
legal I don't like either. They both seem inelegant. Using the for
statement as Lew suggested at least makes sure that the two reads are
close together. This idiom is pretty common and I wonder if it's
worth considering a little bit of syntax that would allow (imho)
cleaner code.

Perhaps something equivalent to the for loop where the action that
takes place at the bottom of the loop in a standard for loop takes
place at the top of the loop. I.e.,
for (a; b; c) {d}
is equivalent to
{
a;
while (b) {
d;
c;
}
}

If we extended the while loop where

while(a; b; c) {d}

is rendered as

{
a;
while (1) {
b;
if (c) {
d;
} else {
break;
}
}
}

Then the original request becomes

while(; line=reader.readLine(); line != null) {
...
}
which avoids both the statement with side effects and duplication
of the readLine().

Of with all three clauses

while (Reader r = getReader(); line=r.readLine(); line != null) {

I think I would use such this rather often were it available. Has
such a construct been implemented in other languages or proposed for
Java?

Regards,
Tom McGlynn

 

[Lew]

That code is fine. There is really no other way to do it. However in
general it is confusing to newbies if you write code of the form:

The code isn't necessarily fine. It puts the scope of 'line' outside the
loop, where in most cases it should be confined to the loop.

There is really another way to do it, posted about eight hours prior to your
post and quoted by the OP. This other way confines the scope of 'line' to the
loop.

 

[Lew]

The problem with this idiom for me is that you have a choice of either
having a statement that has side effects, e.g., the original code, or
you need to duplicate the read statement. While both of these are
legal I don't like either. They both seem inelegant.

"Seem" being the operative term.

There's nothing wrong with writing the 'readLine()' assignment twice, since
that is what purchases the scope confinement for the 'line' variable.

 

[Tom McGlynn]

"Seem" being the operative term.

There's nothing wrong with writing the 'readLine()' assignment twice, since
that is what purchases the scope confinement for the 'line' variable.

For me duplication of code is almost always inelegant and even
slightly dangerous. There's always the chance that there could be
unintended inconsistencies between the two instances--especially when
code gets modified. I make no claim that this is a massive issue, but
neither is the suggested change very large. As with the for
statement it allows restricting the scope of the variables used in
the loop. Given that it's not currently valid it is naturally less
familiar than currently legal idioms. The particular syntax I used is
the result of at least 30 seconds of thought: there is likely
something better, I was interested in the idea not the particular
implementation.

The proposal would address a fairly broad class of loops: whenever the
loop is to be terminated based upon some expression, and the value of
that expression is also needed within the loop.

Regards
Tom McGlynn

 

[Lew]

For me duplication of code is almost always inelegant and even
slightly dangerous. There's always the chance that there could be
unintended inconsistencies between the two instances--especially when
code gets modified. I make no claim that this is a massive issue, but
neither is the suggested change very large.

Copy-and-paste avoids divergence of the duplicated expressions.

Since I don't have a problem with the idiom the OP wrote about, I usually do this:

for ( String line; (line = reader.readLine()) != null; )
{
...
}

This limits the scope of 'line', avoids curly-brace explosion and avoids
unnecessary duplication of code, much like your proposed 'while' syntax except
that it's legal.

 

[Tom Anderson]

Copy-and-paste avoids divergence of the duplicated expressions.

Since I don't have a problem with the idiom the OP wrote about, I usually do
this:

for ( String line; (line = reader.readLine()) != null; )
{
...
}

This limits the scope of 'line', avoids curly-brace explosion and avoids
unnecessary duplication of code, much like your proposed 'while' syntax
except that it's legal.

I like that.

If you had this:

http://urchin.earth.li/~twic/Code/LineIterator.java

You could write:

import static LineIterator.lines;

for (String line: lines(reader)) {
...
}

However, you would throw away your ability to see exceptions, and there's
a bit more runtime overhead.

tom

 

[Tom McGlynn]

I like that.

If you had this:

http://urchin.earth.li/~twic/Code/LineIterator.java

You could write:

import static LineIterator.lines;

for (String line: lines(reader)) {
...

}

However, you would throw away your ability to see exceptions, and there's
a bit more runtime overhead.

tom

Lew's construction may be the best of the bunch using an expression
with side effects. But putting it in a for loop doesn't alter the
fact that there is an expression doing two things as once -- which I
dislike. This situation is pretty much the only time I write code
that includes such expressions. At other times I've used the
duplicate assignment approach -- and occasionally have paid a price
where I missed updating one of them in later on, though it has usually
been quickly detected. I still don't like either approach. It sounds
like Eclipse PMD plugin shares at least some of my prejudices.

Tom's suggestion of the use of an iterator when it's available is very
nice but as he points out the handling of exceptions is an issue. For
me at least this kind of loop comes up in contexts other than I/O.
I'll spend a little more time thinking about if I can build/use an
iterator when it seems appropriate. But it is probably overkill in
most simple cases.

Tom McGlynn