append() vs. write()

[Benjamin Trendelkamp-Schroer]

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.

[Jeff Higgins]

PrintWriter.append(DecimalFormat.format(myFPNumber,null,null))?

[markspace]

On 1/10/2012 8:17 AM, Benjamin Trendelkamp-Schroer wrote:

> 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

Well, no and no. No, Formatter has several constructors with different
arguments, one of which is Appendable.

But also, no you CAN use BufferedWriter because it is an Appendable
also. Double check my reading of the docs but I'm sure that's what it says.

<http://docs.oracle.com/javase/7/docs/api/java/io/BufferedWriter.html>

"All Implemented Interfaces:
Closeable, Flushable, Appendable, AutoCloseable"

So you can just use a BufferedWriter, no problem.

[Jeff Higgins]

I'll try again.

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.Writer;
import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.util.Collection;


public class Scratch {

public static void main(String[] args) throws IOException {

Writer writer = new PrintWriter(
new BufferedWriter(
new FileWriter(args[0])));

String tableHeader, tableFooter,
rowHeader, rowFooter, columnSeparator;

// not intended to compile

Matrix matrix;
MatrixRow row;

writer.append(tableHeader);
while (matrix.hasRows()) {
row = matrix.nextRow();
writer.append(rowHeader);
while (row.hasNextCell()) {
// java.io.Writer has an append method that takes a CharSequence
writer.append(
getCellFormatter(row.rowIndex, row.columnIndex)
//DecimalFormat has a format method that returns a
StringBuilder
//StringBuilder implements CharSequence
.format(row.nextCell().doubleValue(),null,null));
writer.append(columnSeparator);
}
writer.append(rowFooter);
}
writer.append(tableFooter);
}
}

/* probably in your Matrix class

DecimalFormat getCellFormatter(int rowIndex, int columnIndex) {
DecimalFormat formatter =
(DecimalFormat)DecimalFormat.getInstance();
// apply a pattern depending upon row and column
formatter.applyPattern("yourPattern");
return formatter;
}
*/

[Jeff Higgins]

On 01/10/2012 04:48 PM, Jeff Higgins wrote:
> 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".
>>

Oops! java.utilFormatter Duh. Sorry, please ignore previous post.

[Jeff Higgins]

Well,maybe not all is lost.
PrintWriter does have a printf( String format, Object... args).
So I guess you can lose the DecimalFormat for the printf.

[Jeff Higgins]

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.Writer;
import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.util.Collection;


public class Scratch {

public static void main(String[] args) throws IOException {

PrintWriter writer = new PrintWriter(

new BufferedWriter(
new FileWriter(args[0])));

String tableHeader, tableFooter,
rowHeader, rowFooter, columnSeparator;

// not intended to compile

Matrix matrix;
MatrixRow row;

writer.print(tableHeader);

while (matrix.hasRows()) {
row = matrix.nextRow();

writer.print(rowHeader);
while (row.hasNextCell()) {
printFormattedCellValue(

writer,row.nextCell().doubleValue(),row.rowIndex,row.columnIndex);
writer.print(columnSeparator);

}
writer.append(rowFooter);
}
writer.append(tableFooter);
}
}
/* probably in your Matrix class

void printFormattedCellValue(
PrintWriter writer, double value, int rowIndex, int columnIndex) {

// apply a format depending upon rowIndex and columnIndex
String format;
Object[] args;
writer.printf(format,value,args[0]...);
}
*/

[Lew]

Benjamin Trendelkamp-Schroer wrote:
> 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".

Everyone else has provided great answers, especially Jeff Higgins, so I won't
repeat what they said.

> From what I take from the java doc [sic]. 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 [sic] 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

You need to keep reading Javadocs. You missed something, but again others
have pointed it out already.

> large (say 10000 rows and columns) I would have to put each row in an
> appropriately formatted String o0r StringBuffer, calling the append

Why do you insist on 'StringBuffer'? What does the synchronization provide
that you need?

Not that you need it or 'StringBuilder', but I'm curious why you went with
'StringBuffer'.

> 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 [sic]. 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.

You don't know what your performance will be *until* you measure. Have you
measured? If not, why are you worried about performance?

Go with better code and generally you'll see the performance you want.

> 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.

There's no point in excusing flaws at the beginning, because they become bad
habits that then you will have great ego defense over when people criticize
your mistakes, especially the obvious ones. Don't come asking for help and
then ask people not to give it. Every bit of "criticism" you get now will
help you be a better programmer. Far from repelling the feedback, you should
beg for it.

To start with, the language is "Java", not "java", the documentation comments
produce "Javadocs", not "java docs", and you should usually prefer
'StringBuilder' to 'StringBuffer'.

--
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg