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From: Jeff Higgins <jeff@invalid.invalid>
Newsgroups: comp.lang.java.programmer
Subject: Re: append() vs. write()
Date: Tue, 10 Jan 2012 13:14:41 -0500
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On 01/10/2012 11:17 AM, Benjamin Trendelkamp-Schroer wrote:
> Hi,
>
> I want to write a method that can write possibly large matrices of
> floating point numbers in scientific notation to human readable ascii
> files. I want to be able to specify the formatting of the floating
> point numbers usins format strings like "%1.8e" or "%2.5f".
>
>  From what I take from the java doc. I can do something like
>
> i) java.io.File file = new java.io.File(pathnameOfMyFile);
>    java.io.FileWriter fileWriter = new java.io.FileWriter(file);
>    java.util.Formatter f = new java.util.Formatter(fileWriter);
>    for(int i ...){
>       for(int j ...){
>          f.format("%1.8e", Matrix.getEntry(i,j))
>          f.format("%s", columnSeparator)    //columnSeparator = "
> " (for example)
>       }
>       f.format("%s", rowSeparator) // rowSeparator="\n" (for example)
>    }
>
> ii) Use a buffered writer which is adviced as being good practice in
> all tutorials since it has a buffered write method. But as far as I
> understand Formatter does only use the format method of the Appendable
> interface and not the bufered write method. If my Matrix gets very
> large (say 10000 rows and columns) I would have to put each row in an
> appropriately formatted String o0r StringBuffer, calling the append
> method on the StringBuffer through the format method of Formatter many
> times and use write to output it to the buffered writer. But this
> string would be quite large + I would have to create that string and
> the Formatter for each new row (using for example
> StringBuffer.toString(), Formatter(StringBuffer)).
>
> I am asking because I am not sure what is the best practice hear. My
> favorite solution would be to have a method that I could just pass a
> Formatter to so that I could use that formatter object to call other
> methods doing the formatting on the level of single entries of my
> matrix without the need to create a lot of formatter objects. But on
> the other hand I would like to make writing out to files as fast as
> possible and do not want to suffer performance penalties from
> repeatedly calling an append() method where it would be advisable to
> make fewer calls to write with string containing more characters.
>
> I am quite new to Java so I would appreciate any help with that and
> ask you to excuse any obvious mistakes and style flaws that I have
> made.
PrintWriter.append(DecimalFormat.format(myFPNumber,null,null))?