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.
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:
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.
Use getInstance or getNumberInstance to get the
normal 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%.
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 DecimalNumberFormat. 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:
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.
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.
Returns a Long if possible (e.g. within range [Long.MIN_VALUE,
Long.MAX_VALUE], and with no decimals), otherwise a Double.
If IntegerOnly is set, will stop at a decimal
point (or equivalent; e.g. for rational numbers "1 2/3", will stop
after the 1).
Does not throw an exception; if no object can be parsed, index is
unchanged!
Returns true if this format will parse numbers as integers only.
For example in the English locale, with ParseIntegerOnly true, the
string "1234." would be parsed as the integer value 1234 and parsing
would stop at the "." character. Of course, the exact format accepted
by the parse operation is locale dependant and determined by sub-classes
of NumberFormat.
Returns the default number format for the current default locale.
The default format is one of the styles provided by the other
factory methods: getNumberInstance, getCurrencyInstance or getPercentInstance.
Exactly which one is locale dependant.
Returns the default number format for the specified locale.
The default format is one of the styles provided by the other
factory methods: getNumberInstance, getCurrencyInstance or getPercentInstance.
Exactly which one is locale dependant.
Returns true if grouping is used in this format. For example, in the
English locale, with grouping on, the number 1234567 might be formatted
as "1,234,567". The grouping separator as well as the size of each group
is locale dependant and is determined by sub-classes of NumberFormat.
Sets the maximum number of digits allowed in the integer portion of a
number. maximumIntegerDigits must be >= minimumIntegerDigits. If the
new value for maximumIntegerDigits is less than the current value
of minimumIntegerDigits, then minimumIntegerDigits will also be set to
the new value.
Sets the minimum number of digits allowed in the integer portion of a
number. minimumIntegerDigits must be <= maximumIntegerDigits. If the
new value for minimumIntegerDigits exceeds the current value
of maximumIntegerDigits, then maximumIntegerDigits will also be set to
the new value
public void setMaximumFractionDigits(int newValue)
Sets the maximum number of digits allowed in the fraction portion of a
number. maximumFractionDigits must be >= minimumFractionDigits. If the
new value for maximumFractionDigits is less than the current value
of minimumFractionDigits, then minimumFractionDigits will also be set to
the new value.
public void setMinimumFractionDigits(int newValue)
Sets the minimum number of digits allowed in the fraction portion of a
number. minimumFractionDigits must be <= maximumFractionDigits. If the
new value for minimumFractionDigits exceeds the current value
of maximumFractionDigits, then maximumIntegerDigits will also be set to
the new value
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