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Re: Strange JTable issue in Sun's Java code

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Jeff Higgins <jeff@invalid.invalid> wrote in
news:jf3amd$1rr$1@dont-email.me: 

> On 01/16/2012 08:48 PM, Novice wrote:
> 
>>
>> I've just stepped through the whole removeEntries() method until it
>> crashed.
> 
> OK, your program crashes inside the removeEntries method - just as the
> stack trace indicated.
> 
> I should mention that I downloaded a Java 1.7 JDK and JRE and I'm
>> using _that_ version now. The code for this method looks the same but
>> I might be missing a subtle difference. Here's the code, along with
>> what I saw as I stepped through it:
> 
> One way to decide on an update - I'm using Java 6.
> 
Since Java 7 didn't change anything except the line number (the failing 
line number is 400 in Java 7), I've reverted to running Java 6.18.
>>
>>      public void removeEntries(int start, int length) {
>> //Before executing the following line, start and length both show
>> "cannot //be resolved to a variable". When I tried setting them as
>> expressions in //the expressions monitor, I got
>> "<error(s)_during_the_evaluation>" for //both variables
> 
> Have you disabled debug information in your project build settings?
> 
I've looked around and I'm not finding any such settings. Can you please 
be specific on which menu I should check and which specific settings I'd 
have had to mess with? (I don't think I've EVER messed with the debug 
settings but I might as well look, just in case I did at some point and 
forgot. Or a new version of Eclipse had unexpected values for some 
settings.)

>>          int sizes[] = getSizes();
>> //getSizes() returns an int array of 45 items; each item has a value
>> of //21
>> //when I inspect or inspect 'sizes' (without the brackets), I get
>> "sizes //cannot be resolved to a variable. It's not clear if the
>> assignment has //worked!
>> //Before this next line, 'start' and 'length' are still "cannot be
>> //resolved to a variable."
>>          int end = start + length;
>> //After the assignment, 'end' "cannot be resolved to a variable"
>> //Before this next line, 'a' is an int array of 45 diverse integers
>> and //'a.length is 45. 'length' "cannot be resolved to a variable"
>>          int n = a.length - length;
>> //After the preceding statement is executed, 'n' "cannot be resolved
>> to a //variable"
>>          a = new int[n];
>> //After the preceding statement is executed, 'a' has a value of "[]"
>> (!!) 
>>          for (int i = 0; i<  start; i++) {
>> //Before the following line is executed the first time, 'i' should be
>> zero //but Eclipse says "i cannot be resolved to a variable".
>> 'sizes[i] cannot //be resolved to a variable".
>>              a[i] = sizes[i] ;
>> //Upon executing the preceding line the first time through the loop,
>> we get //the ArrayIndexOutOfBoundsException for an index value of 0
> 
> Using the SSCCE that I provided elsethread, I can get your method to 
> crash at the above line also. I cannot remember with what combinations
> of values.
> 
>>          }
>>          for (int i = start; i<  n; i++) {
>>              a[i] = sizes[i+length] ;
>>          }
>>          setSizes(a);
>>      }
>>
When I used your SSCCE, it crashed at line 44 (a = new int[n];) which is 
just above that point. I'm not sure what the significance of that is 
though. I'm really not quite sure what your SSCCE is trying to do.

For what it's worth, I created my own SSCCE which is somewhat longer than 
yours but more closely parallels what my problem code is doing. It works 
fine though. It doesn't crash and I'm not getting any of the "cannot be 
resolved to a variable" nonsense when I try to debug. I put my SSCCE (and 
yours) in the same project as the one that is blowing up so they must be 
using the same settings/compiler/etc. 

>>
>> This seems REALLY messed up to me. I don't understand why all these
>> variables "cannot be resolved to a variable". If they really don't
>> have values, why doesn't it crash long before we get to the line
>> where we get the exception? But if the variables do have values, why
>> can't Eclipse show them to me?
>>
>> Since a newer JDK/JRE didn't resolve the problem and it happens
>> consistently, I'm leaning toward Eclipse as being the problem here. I
>> can't think of anything inappropriate that I'm doing in my code and I
>> have to believe that the Java team tests these methods pretty
>> thoroughly before putting them in a JDK.
> 
> You could try another IDE, but that seems drastic.
> Another option, you could employ javac and jdb outside the IDE.
> 
Can you flesh that out a bit. I have used raw javac a long time ago 
before I got my first proper editor but I'm not sure what that and jdb 
will prove here. Are we just trying to establish whether Eclipse and it's 
compiler are the culprits?
 
>>
>> Am I thinking along the right lines here? If so, what do I do next?
>> I'd like my program to work without getting this apparently
>> inappropriate exception but I'm not sure how to accomplish that....
> 
> I'd take a deep breath, relax, become intimate with my debugger, and
> enjoy. Really, try compiling and running the SSCCE I provided - do you
> get the variable not resolved?

Your SSCCE has VERY different behavior than mine.

Yours actually has values for all of the variables until well into the 
method. 'start' and 'length' begin as 0 and 3 respectively. getSizes() 
initially contains [1, 2, 3, 4, 5]. 'getSizes.length' is 5. 'a' is empty. 
After "int[] sizes = getSize();", 'sizes' contains [1,2,3,4,5]. 
'a.length' is 0. 'length' remains 3. 'n' is -3. (0-3). Not surprisingly, 
Java doesn't like the line "a = int[n]" when n is -3 and this causes the 
exception just before we get to the first loop. 

I've just tried my code again but it's still doing the same nonsense as 
before. 'getSizes()' actually returns a very reasonable array but after 
assigning it to 'sizes', I get the "cannot be resolved to a variable" 
message again. 'start' and 'length' have the same issues on entry to the 
method. And so it goes until the first iteration of the first loop when 
it crashes again on the ArrayIndexOutOfBoundsException because the index 
is 0. 

I can't figure out if "cannot be resolved to a variable" proves that the 
debugger is messed up or if it is only masking the underlying error. 
Maybe something that should be in scope isn't for some reason??

> One question. Why arrays here, instead of ArrayLists? The answer would
> probably be obvious knowing the rest of your code.

I don't honestly know. My table model actually consists of a Vector of 
rows, not an array or a Vector of Vectors. The rows being stored in the 
Vector have their own custom class that consists of three String fields, 
one for each of the columns of the JTable. The list of column names to be 
used in the header is an array but that's just about the only one in the 
entire program, aside from some local ones used to determine the widest 
values in each column. 

getSizes() is getting an array of 45 entries and that surely corresponds 
to the number of rows in the table. From looking at getSizes(), it seems 
as if it might be keeping track of sizes of cells or something like that. 

--
One strange thing jumped out at me when I was debugging my code just now. 
A System.out.println() that I'd put into another method for a couple of 
minutes and then deleted is still being executed when I do that method 
(which sets the column widths of the table). That is REALLY bizarre and 
suggests that I'm executing a slightly older version of the program. I 
don't see how that bears on exception I'm getting but it may point to the 
solution anyway: if I actually executed the code I want to execute, maybe 
the exception wouldn't be happening. Why would the debugger execute a 
different version of the code than it is displaying??

--
Rhino

















-- 
Novice

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Thread

Strange JTable issue in Sun's Java code Novice <novice@example..com> - 2012-01-16 18:34 +0000
  Re: Strange JTable issue in Sun's Java code Jeff Higgins <jeff@invalid.invalid> - 2012-01-16 14:48 -0500
    Re: Strange JTable issue in Sun's Java code Jeff Higgins <jeff@invalid.invalid> - 2012-01-16 14:55 -0500
    Re: Strange JTable issue in Sun's Java code Jeff Higgins <jeff@invalid.invalid> - 2012-01-16 15:19 -0500
      Re: Strange JTable issue in Sun's Java code Jeff Higgins <jeff@invalid.invalid> - 2012-01-16 15:31 -0500
        Re: Strange JTable issue in Sun's Java code Jeff Higgins <jeff@invalid.invalid> - 2012-01-16 17:57 -0500
    Re: Strange JTable issue in Sun's Java code Novice <novice@example..com> - 2012-01-17 01:48 +0000
      Re: Strange JTable issue in Sun's Java code Jeff Higgins <jeff@invalid.invalid> - 2012-01-17 03:22 -0500
        Re: Strange JTable issue in Sun's Java code Jeff Higgins <jeff@invalid.invalid> - 2012-01-17 03:29 -0500
        Re: Strange JTable issue in Sun's Java code Jeff Higgins <jeff@invalid.invalid> - 2012-01-17 03:49 -0500
        Re: Strange JTable issue in Sun's Java code Jeff Higgins <jeff@invalid.invalid> - 2012-01-17 03:55 -0500
        Re: Strange JTable issue in Sun's Java code Novice <novice@example..com> - 2012-01-17 22:21 +0000
          Re: Strange JTable issue in Sun's Java code Jeff Higgins <jeff@invalid.invalid> - 2012-01-17 18:18 -0500
            Re: Strange JTable issue in Sun's Java code Jeff Higgins <jeff@invalid.invalid> - 2012-01-17 20:56 -0500
              Re: Strange JTable issue in Sun's Java code Novice <novice@example..com> - 2012-01-18 05:24 +0000
                Re: Strange JTable issue in Sun's Java code Novice <novice@example..com> - 2012-01-18 17:40 +0000
            Re: Strange JTable issue in Sun's Java code Novice <novice@example..com> - 2012-01-18 05:37 +0000
  Re: Strange JTable issue in Sun's Java code Christian Kaufhold <chka@ucuri.chka.de> - 2012-01-19 21:00 +0100

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