Class NumberConverter 

java.lang.Object
   |
   +----NumberConverter
public class NumberConverter
extends Object
This class is just a trivial demo of how to do conversions between strings and numbers in a fully WORA (Write Once Run Anywhere) way. Java's BigDecimal class and my own BDFormat class are used (instead of Java's Double, Long and NumberFormat classes) for two main reasons.

1. Double and Long store numbers as binaries, creating subtle pitfalls and limits with which a programmer using those classes must become familiar if unintended results are to be avoided. While Double and Long perform better (they take advantage of the CPU's floating point routines), speed in financial and arithmetic operations is rarely as important as accuracy.

2. NumberFormat has two major limitations in its current form: its format() routine does not handle BigDecimal objects correctly, and its parse() routine does not treat spaces correctly in locales that use the space as a grouping separator. My BDFormat class makes extensive use of NumberFormat's format() and parse() methods but adds the functionality to fix both these problems. Also, an attempt to format() a number too large for NumberFormat will now throw an exception instead of just quietly returning incorrect output.

Finally, a greatly imporved BigDecimal class is now available as com.ibm.math.BigDecimal. It's up to 23-times faster and it does decimal arithmetic in a way humans (other than numerics specialists) would expect. Get it from IBM alphaWorks.

To use this class (while you get used to Java's "new math" as I see it), just instantiate (assign a variable to) NumberConverter and call one of the methods, as in:
BigDecimal big = new BigDecimal( someNumber );
String str = new NumberConverter().writeDecimal( big );
or
Locale loc_fr = new Locale( "fr", "FR" );
String input = "-12 345,678 Fr";
BigDecimal bd_in = new NumberConverter(loc).readInteger( input );
// bd_in now contains a BigDecimal whose value is -12346 (after rounding)

To use the BDFormat class directly (once you are comfortable with this "new math"), instantiate BDFormat and call one of the methods. For example, to display an amount in several currencies, with decimals aligned in a 30-column field, you can write: 
BigDecimal dollarAmount = new BigDecimal( amountAsDoubleOrString );
BigDecimal francsPerDollar = new BigDecimal(5.6755);
BigDecimal liraPerDollar = new BigDecimal(1676.00);
BigDecimal kronerPerDollar = new BigDecimal(6.4310);
// if using System.out, and en_US is the default locale, you can write:
System.out.println(
"Soccer tickets........." + new BDFormat().curformat( dollarAmount, 30) + "\n"
+"Billets du football...." + new BDFormat( new Locale("fr","FR") ).curformat(
dollarAmount.multiply(francsPerDollar), 30) + "\n"
+"Biglietti di soccer...." + new BDFormat( new Locale("it","IT") ).curformat(
dollarAmount.multiply(liraPerDollar), 30) + "\n"
+"Fodboldbilletter......." + new BDFormat( new Locale("da","DK") ).curformat(
dollarAmount.multiply(kronerPerDollar), 30)  );
which gives the output:
Soccer tickets.......................... $195.28
Billets du football.................... 1 108,31 F
Biglietti di soccer............... L. 327.289
Fodboldbilletter.................... kr 1.255,85

Version:
1.0 - November 1998
Author:
Tooy Dahlman

Variable Index

o nf
The BigDecimal number formatter.
o roundingMode
The usual rounding mode for financial apps, known as "HALF_EVEN".

Constructor Index

o NumberConverter()
Default constructor, uses the default locale.
o NumberConverter(Locale)
Locale-specific constructor.

Method Index

o main(String[])
Test routine: try out the parsing and formatting methods.
o readDecimal(String)
Get a BigDecimal from the string you supply.
o readInteger(String)
Get a BigDecimal (less any decimal fraction) from the string you supply.
o writeDecimal(BigDecimal)
Get a formatted string from the BigDecimal amount you supply.
o writeInteger(BigDecimal)
Get a formatted string from the BigDecimal amount you supply.

Variables

o nf 
 private BDFormat nf
The BigDecimal number formatter.

o roundingMode 
 private int roundingMode
The usual rounding mode for financial apps, known as "HALF_EVEN".

Constructors

o NumberConverter 
 public NumberConverter()
Default constructor, uses the default locale.

o NumberConverter 
 public NumberConverter(Locale loc)
Locale-specific constructor.

Methods

o readInteger 
 public BigDecimal readInteger(String input)
Get a BigDecimal (less any decimal fraction) from the string you supply.

o readDecimal 
 public BigDecimal readDecimal(String input)
Get a BigDecimal from the string you supply.

o writeInteger 
 public String writeInteger(BigDecimal amount)
Get a formatted string from the BigDecimal amount you supply.

o writeDecimal 
 public String writeDecimal(BigDecimal amount)
Get a formatted string from the BigDecimal amount you supply.

o main 
 public static void main(String args[]) throws IOException
Test routine: try out the parsing and formatting methods.