Java Doc for NumberFormat.java in  » Internationalization-Localization » icu4j » com » ibm » icu » text » Java Source Code / Java DocumentationJava Source Code and Java Documentation

This is an enhanced version of NumberFormat that is based on the standard version in the JDK. New or changed functionality is labeled NEW or CHANGED.

NumberFormat helps you to format and parse numbers for any locale. Your code can be completely independent of the locale conventions for decimal points, thousands-separators, or even the particular decimal digits used, or whether the number format is even decimal.

To format a number for the current Locale, use one of the factory class methods:

 myString = NumberFormat.getInstance().format(myNumber);
 

 NumberFormat nf = NumberFormat.getInstance();
 for (int i = 0; i < a.length; ++i) {
 output.println(nf.format(myNumber[i]) + "; ");
 }
 

 NumberFormat nf = NumberFormat.getInstance(Locale.FRENCH);
 

 myNumber = nf.parse(myString);
 

You can also control the display of numbers with such methods as setMinimumFractionDigits. If you want even more control over the format or parsing, or want to give your users more control, you can try casting the NumberFormat you get from the factory methods to a DecimalFormat. This will work for the vast majority of locales; just remember to put it in a try block in case you encounter an unusual one.

NumberFormat is designed such that some controls work for formatting and others work for parsing. The following is the detailed description for each these control methods,

setParseIntegerOnly : only affects parsing, e.g. if true, "3456.78" -> 3456 (and leaves the parse position just after '6') if false, "3456.78" -> 3456.78 (and leaves the parse position just after '8') This is independent of formatting. If you want to not show a decimal point where there might be no digits after the decimal point, use setDecimalSeparatorAlwaysShown on DecimalFormat.

You can also use forms of the parse and format methods with ParsePosition and FieldPosition to allow you to:

• progressively parse through pieces of a string
• align the decimal point and other areas

1. If you are using a monospaced font with spacing for alignment, you can pass the FieldPosition in your format call, with field = INTEGER_FIELD. On output, getEndIndex will be set to the offset between the last character of the integer and the decimal. Add (desiredSpaceCount - getEndIndex) spaces at the front of the string.
2. If you are using proportional fonts, instead of padding with spaces, measure the width of the string in pixels from the start to getEndIndex. Then move the pen by (desiredPixelWidth - widthToAlignmentPoint) before drawing the text. It also works where there is no decimal, but possibly additional characters at the end, e.g., with parentheses in negative numbers: "(12)" for -12.

Synchronization

Number formats are generally not synchronized. It is recommended to create separate format instances for each thread. If multiple threads access a format concurrently, it must be synchronized externally.

DecimalFormat

DecimalFormat is the concrete implementation of NumberFormat, and the NumberFormat API is essentially an abstraction from DecimalFormat's API. Refer to DecimalFormat for more information about this API.

• Leading zeros
  '00', '0123' fail the parse, but '0' and '0.001' pass
• Leading or doubled grouping separators
  ',123' and '1,,234" fail
• Groups of incorrect length when grouping is used
  '1,23' and '1234,567' fail, but '1234' passes
• Grouping separators used in numbers followed by exponents
  '1,234E5' fails, but '1234E5' and '1,234E' pass ('E' is not an exponent when not followed by a number)