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

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

If you are formatting multiple numbers, it is more efficient to get the format and use it multiple times so that the system doesn't have to fetch the information about the local language and country conventions multiple times.

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

To format a number for a different Locale, specify it in the call to getInstance.

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

You can also use a NumberFormat to parse numbers:

myNumber = nf.parse(myString);

Use getInstance or getNumberInstance to get the normal number format. Use getIntegerInstance to get an integer number format. Use getCurrencyInstance to get the currency number format. And use getPercentInstance to get a format for displaying percentages. Some factory methods are found within subclasses of NumberFormat. With this format, a fraction like 0.53 is displayed as 53%.

Starting from ICU 4.2, you can use getInstance() by passing in a 'style' as parameter to get the correct instance. For example, use getInstance(...NUMBERSTYLE) to get the normal number format, getInstance(...PERCENTSTYLE) to get a format for displaying percentage, getInstance(...SCIENTIFICSTYLE) to get a format for displaying scientific number, getInstance(...INTEGERSTYLE) to get an integer number format, getInstance(...CURRENCYSTYLE) to get the currency number format, in which the currency is represented by its symbol, for example, "$3.00". getInstance(...ISOCURRENCYSTYLE) to get the currency number format, in which the currency is represented by its ISO code, for example "USD3.00". getInstance(...PLURALCURRENCYSTYLE) to get the currency number format, in which the currency is represented by its full name in plural format, for example, "3.00 US dollars" or "1.00 US dollar".

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

For example, you can align numbers in two ways:

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.

see DecimalFormat see java.text.ChoiceFormat