Fortran I/O Descriptors in Java?

Question

I'm currently having to interface with a legacy Fortran program by creating an ascii output file that the program needs to read in, perform some calculations, and then I have to parse the binary output. For the most part, I have this working, but I'm running into a slight snag.

The problem I'm running into is with Fortran descriptors. Is there an easy way I can get a descriptor like E9.3 into a DecimalFormat object in Java?

The DecimalFormat I have works only for numbers less than 1. For numbers < 1 such as 0.123, they are written out with the sign on the exponential, as 1.230E-01. However, for numbers greater than 1 (12.345), they are written out as 1.234E01 rather than 1.234E+01. From what I'm being told, the program is expecting that '+' sign as part of the exponential.

The DecimalFormat string I'm currently using is "#0.000E00", and I'm currently pulling some string manipulation to insert the '+' in there (after the E but before the digits) if necessary. There has to be a better way to do this. Any assistance would be appreciated.

Answer 1

Are you really sure you need this? Maybe it's only a compiler extension, but it's worth checking if the Fortran program actually accepts your form 1.234E01. My both compilers (gfortran and Solaris Studio) do accept them with E9.3 edit descriptor.

Answer 2

If you have access to the source of the fortran program, you could change it to read the input file using the * descriptor, e.g. if you read in an array data of n values, e.g. change this:

read(iUnit,'(10E9.3)') data(10)

to something like:

read(iUnit, *) data(10)

or to write the file unformatted and then read in the binary data.

Answer 3

If you need the whole string to be 9 characters, it means there'll be three characters left for the decimal part. You can express this with printf style formatting like this:

groovy:000> String.format("%.3E", 0.000123456789)         
===> 1.235E-04
groovy:000> String.format("%.3E", 1234.56789)         
===> 1.235E+03

If you need it to be nine characters in total even for negative numbers, with the leading '-' counting against the character count, you'll have to us an if to use a different format for negative numbers.