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creating an exception

Posted on 2003-11-28
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Last Modified: 2010-03-31
i have a data file filled with records and i need to create an exception for when a record isn't found.  i figure that it won't be found if the end of file has been reached before finding it.  so in my exception class, would i just extend the ioexception class and then in my method code to retrieve a record, catch an eofexception and throw my exception in its catch block?
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Question by:abstractionz
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Expert Comment

by:CEHJ
ID: 9839448
Just create a subclass of Exception.

if (recordNotFound) {
    throw new RecordNotFoundException("Not found!");
}
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Author Comment

by:abstractionz
ID: 9839475
you have the conditional if(recordNotFound).  how do i know when the end of file has been reached so i can throw my exception, other than catching an end of file exception?
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Expert Comment

by:CEHJ
ID: 9839495
If the loop in which you are reading the file has finished and it has not flagged recordNotFound = false during its execution, then throw one.
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Author Comment

by:abstractionz
ID: 9839502
theres no loop though.  it reads the specified record number.
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LVL 86

Expert Comment

by:CEHJ
ID: 9839525
In that case

if (recordRead.equals(recordToFind) == false) {
    throw ...
}
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Author Comment

by:abstractionz
ID: 9839566
its kind of hard to check that condition.  there's only a record number supplied which helps jump to the correct byte position to retrieve the record.
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Author Comment

by:abstractionz
ID: 9839573
thats why i was thinking of throwing my exception when i catch an eofexception
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LVL 86

Expert Comment

by:CEHJ
ID: 9839596
I don't understand. If you have an offset at which to read a record there shouldn't be any possibility of reaching EOF if the code is correct.
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Author Comment

by:abstractionz
ID: 9839610
the number of records is unknown but lets say there are 25.  if the record number supplied is 30, then there will be an eofexception, because to get to that record the number of bytes i skip is the record number * the number of bytes in a record
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Author Comment

by:abstractionz
ID: 9839612
so it's for record numbers that don't exist
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LVL 86

Accepted Solution

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CEHJ earned 125 total points
ID: 9839651
>>the number of records is unknown

Presumably, you know

a. the size of the file
b. the size of a record

The number of records = filesize/recordsize
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Author Comment

by:abstractionz
ID: 9839659
i never thought of that.  nice.  how do i get the filesize?
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LVL 92

Expert Comment

by:objects
ID: 9839669
try
{
   // look for record
}
catch (EOFException ex)
{
   throw new RecordNotFoundException();
}
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Author Comment

by:abstractionz
ID: 9839673
yea that's the code i originally thought of writing
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LVL 86

Expert Comment

by:CEHJ
ID: 9839742
It's not particularly good to deliberately cause excepetions
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Expert Comment

by:objects
ID: 9839783
> It's not particularly good to deliberately cause excepetions

It may not be deliberately caused.
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Author Comment

by:abstractionz
ID: 9839787
is there a function to get the total number of bytes in a file?
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LVL 86

Expert Comment

by:CEHJ
ID: 9839807
Exceptions, by definition, are concerned with unforeseen conditions in a program. The potential absence of a record is not such a condition. It's a perfectly normal outcome of a normal run of a program and should not cause an exception.
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LVL 86

Expert Comment

by:CEHJ
ID: 9839811
long fileLength = file.length();
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Author Comment

by:abstractionz
ID: 9839836
thanks. i'm going to go with your suggestion cehj.  it will help me with my exception and also in the future when i need to get the record number of a record i have just added somewhere in the file.
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LVL 86

Expert Comment

by:CEHJ
ID: 9839862
8-)
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