NumberFormat (Java Platform SE 8 )

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NumberFormat is the abstract base class for all number
formats. This class provides the interface for formatting and parsing
numbers. NumberFormat also provides methods for determining
which locales have number formats, and what their names are.

is the abstract base class for all number formats. This class provides the interface for formatting and parsing numbers.also provides methods for determining which locales have number formats, and what their names are.

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);

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 < myNumber.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. With this format, a fraction like
0.53 is displayed as 53%.

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.To format a number for a different Locale, specify it in the call toYou can also use ato parse numbers:Useorto get the normal number format. Useto get an integer number format. Useto get the currency number format. And useto get a format for displaying percentages. With this format, a fraction like 0.53 is displayed as 53%.

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 and DecimalFormat are 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 index 6)
if false, “3456.78” → 3456.78 (and leaves the parse position just after index 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.

setDecimalSeparatorAlwaysShown : only affects formatting, and only where
there might be no digits after the decimal point, such as with a pattern
like “#,##0.##”, e.g.,
if true, 3456.00 → “3,456.”
if false, 3456.00 → “3456”
This is independent of parsing. If you want parsing to stop at the decimal
point, use setParseIntegerOnly.

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.

For example, you can align numbers in two ways:

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.

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