public abstract class

NumberFormat

extends Format
java.lang.Object
   ↳ java.text.Format
     ↳ java.text.NumberFormat
Known Direct Subclasses

Class Overview

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: 

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

You can also control the display of numbers with methods such 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. For example, setParseIntegerOnly only affects parsing: If set to true, "3456.78" is parsed as 3456 (and leaves the parse position just after '6'); if set to false, "3456.78" is parsed as 3456.78 (and leaves the parse position just after '8'). This is independent of formatting.

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 to 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. This also works where there is no decimal but possibly additional characters before or after the number, for example 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 of DecimalFormat's API. Refer to DecimalFormat for more information about this API.

See Also

Summary

Nested Classes
class NumberFormat.Field The instances of this inner class are used as attribute keys and values in AttributedCharacterIterator that the formatToCharacterIterator(Object) method returns. 
Constants
int FRACTION_FIELD Field constant identifying the fractional part of a number.
int INTEGER_FIELD Field constant identifying the integer part of a number.
Public Constructors
NumberFormat()
Constructs a new instance of NumberFormat.
Public Methods
Object clone()
Returns a new NumberFormat with the same properties as this NumberFormat.
boolean equals(Object object)
Compares the specified object to this number format and indicates if they are equal.
final String format(long value)
Formats the specified long using the rules of this number format.
final String format(double value)
Formats the specified double using the rules of this number format.
StringBuffer format(Object object, StringBuffer buffer, FieldPosition field)
Formats the specified object as a string using the pattern of this number format and appends the string to the specified string buffer.
abstract StringBuffer format(double value, StringBuffer buffer, FieldPosition field)
Formats the specified double value as a string using the pattern of this number format and appends the string to the specified string buffer.
abstract StringBuffer format(long value, StringBuffer buffer, FieldPosition field)
Formats the specified long value as a string using the pattern of this number format and appends the string to the specified string buffer.
static Locale[] getAvailableLocales()
Gets the list of installed locales which support NumberFormat.
Currency getCurrency()
Returns the currency used by this number format.
final static NumberFormat getCurrencyInstance()
Returns a NumberFormat for formatting and parsing currency values for the default locale.
static NumberFormat getCurrencyInstance(Locale locale)
Returns a NumberFormat for formatting and parsing currency values for the specified locale.
final static NumberFormat getInstance()
Returns a NumberFormat for formatting and parsing numbers for the default locale.
static NumberFormat getInstance(Locale locale)
Returns a NumberFormat for formatting and parsing numbers for the specified locale.
static NumberFormat getIntegerInstance(Locale locale)
Returns a NumberFormat for formatting and parsing integers for the specified locale.
final static NumberFormat getIntegerInstance()
Returns a NumberFormat for formatting and parsing integers for the default locale.
int getMaximumFractionDigits()
Returns the maximum number of fraction digits that are printed when formatting.
int getMaximumIntegerDigits()
Returns the maximum number of integer digits that are printed when formatting.
int getMinimumFractionDigits()
Returns the minimum number of fraction digits that are printed when formatting.
int getMinimumIntegerDigits()
Returns the minimum number of integer digits that are printed when formatting.
static NumberFormat getNumberInstance(Locale locale)
Returns a NumberFormat for formatting and parsing numbers for the specified locale.
final static NumberFormat getNumberInstance()
Returns a NumberFormat for formatting and parsing numbers for the default locale.
final static NumberFormat getPercentInstance()
Returns a NumberFormat for formatting and parsing percentage values for the default locale.
static NumberFormat getPercentInstance(Locale locale)
Returns a NumberFormat for formatting and parsing percentage values for the specified locale.
int hashCode()
Returns an integer hash code for this object.
boolean isGroupingUsed()
Indicates whether this number format formats and parses numbers using a grouping separator.
boolean isParseIntegerOnly()
Indicates whether this number format only parses integer numbers.
Number parse(String string)
Parses a Number from the specified string using the rules of this number format.
abstract Number parse(String string, ParsePosition position)
Parses a Number from the specified string starting at the index specified by position.
final Object parseObject(String string, ParsePosition position)
Parses the specified string starting at the index specified by position.
void setCurrency(Currency currency)
Sets the currency used by this number format when formatting currency values.
void setGroupingUsed(boolean value)
Sets whether this number format formats and parses numbers using a grouping separator.
void setMaximumFractionDigits(int value)
Sets the maximum number of fraction digits that are printed when formatting.
void setMaximumIntegerDigits(int value)
Sets the new maximum count of integer digits that are printed when formatting.
void setMinimumFractionDigits(int value)
Sets the minimum number of fraction digits that are printed when formatting.
void setMinimumIntegerDigits(int value)
Sets the minimum number of integer digits that are printed when formatting.
void setParseIntegerOnly(boolean value)
Specifies if this number format should parse numbers only as integers or else as any kind of number.
[Expand]
Inherited Methods
From class java.text.Format
From class java.lang.Object

Constants

public static final int FRACTION_FIELD

Since: API Level 1

Field constant identifying the fractional part of a number.

Constant Value: 1 (0x00000001)

public static final int INTEGER_FIELD

Since: API Level 1

Field constant identifying the integer part of a number.

Constant Value: 0 (0x00000000)

Public Constructors

public NumberFormat ()

Since: API Level 1

Constructs a new instance of NumberFormat.

Public Methods

public Object clone ()

Since: API Level 1

Returns a new NumberFormat with the same properties as this NumberFormat.

Returns
  • a shallow copy of this NumberFormat.
See Also

public boolean equals (Object object)

Since: API Level 1

Compares the specified object to this number format and indicates if they are equal. In order to be equal, object must be an instance of NumberFormat with the same pattern and properties.

Parameters
object the object to compare with this object.
Returns
  • true if the specified object is equal to this number format; false otherwise.
See Also

public final String format (long value)

Since: API Level 1

Formats the specified long using the rules of this number format.

Parameters
value the long to format.
Returns
  • the formatted string.

public final String format (double value)

Since: API Level 1

Formats the specified double using the rules of this number format.

Parameters
value the double to format.
Returns
  • the formatted string.

public StringBuffer format (Object object, StringBuffer buffer, FieldPosition field)

Since: API Level 1

Formats the specified object as a string using the pattern of this number format and appends the string to the specified string buffer.

If the field member of field contains a value specifying a format field, then its beginIndex and endIndex members will be updated with the position of the first occurrence of this field in the formatted text.

Parameters
object the object to format, must be a Number.
buffer the target string buffer to append the formatted number to.
field on input: an optional alignment field; on output: the offsets of the alignment field in the formatted text.
Returns
  • the string buffer.
Throws
IllegalArgumentException if object is not an instance of Number.

public abstract StringBuffer format (double value, StringBuffer buffer, FieldPosition field)

Since: API Level 1

Formats the specified double value as a string using the pattern of this number format and appends the string to the specified string buffer.

If the field member of position contains a value specifying a format field, then its beginIndex and endIndex members will be updated with the position of the first occurrence of this field in the formatted text.

Parameters
value the double to format.
buffer the target string buffer to append the formatted double value to.
field on input: an optional alignment field; on output: the offsets of the alignment field in the formatted text.
Returns
  • the string buffer.

public abstract StringBuffer format (long value, StringBuffer buffer, FieldPosition field)

Since: API Level 1

Formats the specified long value as a string using the pattern of this number format and appends the string to the specified string buffer.

If the field member of position contains a value specifying a format field, then its beginIndex and endIndex members will be updated with the position of the first occurrence of this field in the formatted text.

Parameters
value the long to format.
buffer the target string buffer to append the formatted long value to.
field on input: an optional alignment field; on output: the offsets of the alignment field in the formatted text.
Returns
  • the string buffer.

public static Locale[] getAvailableLocales ()

Since: API Level 1

Gets the list of installed locales which support NumberFormat.

Returns
  • an array of locales.

public Currency getCurrency ()

Since: API Level 1

Returns the currency used by this number format.

This implementation throws UnsupportedOperationException, concrete subclasses should override this method if they support currency formatting.

Returns
  • the currency that was set in getInstance() or in setCurrency(), or null.
Throws
UnsupportedOperationException

public static final NumberFormat getCurrencyInstance ()

Since: API Level 1

Returns a NumberFormat for formatting and parsing currency values for the default locale.

Returns
  • a NumberFormat for handling currency values.

public static NumberFormat getCurrencyInstance (Locale locale)

Since: API Level 1

Returns a NumberFormat for formatting and parsing currency values for the specified locale.

Parameters
locale the locale to use.
Returns
  • a NumberFormat for handling currency values.

public static final NumberFormat getInstance ()

Since: API Level 1

Returns a NumberFormat for formatting and parsing numbers for the default locale.

Returns
  • a NumberFormat for handling Number objects.

public static NumberFormat getInstance (Locale locale)

Since: API Level 1

Returns a NumberFormat for formatting and parsing numbers for the specified locale.

Parameters
locale the locale to use.
Returns
  • a NumberFormat for handling Number objects.

public static NumberFormat getIntegerInstance (Locale locale)

Since: API Level 1

Returns a NumberFormat for formatting and parsing integers for the specified locale.

Parameters
locale the locale to use.
Returns
  • a NumberFormat for handling integers.

public static final NumberFormat getIntegerInstance ()

Since: API Level 1

Returns a NumberFormat for formatting and parsing integers for the default locale.

Returns
  • a NumberFormat for handling integers.

public int getMaximumFractionDigits ()

Since: API Level 1

Returns the maximum number of fraction digits that are printed when formatting. If the maximum is less than the number of fraction digits, the least significant digits are truncated.

Returns
  • the maximum number of fraction digits.

public int getMaximumIntegerDigits ()

Since: API Level 1

Returns the maximum number of integer digits that are printed when formatting. If the maximum is less than the number of integer digits, the most significant digits are truncated.

Returns
  • the maximum number of integer digits.

public int getMinimumFractionDigits ()

Since: API Level 1

Returns the minimum number of fraction digits that are printed when formatting.

Returns
  • the minimum number of fraction digits.

public int getMinimumIntegerDigits ()

Since: API Level 1

Returns the minimum number of integer digits that are printed when formatting.

Returns
  • the minimum number of integer digits.

public static NumberFormat getNumberInstance (Locale locale)

Since: API Level 1

Returns a NumberFormat for formatting and parsing numbers for the specified locale.

Parameters
locale the locale to use.
Returns
  • a NumberFormat for handling Number objects.

public static final NumberFormat getNumberInstance ()

Since: API Level 1

Returns a NumberFormat for formatting and parsing numbers for the default locale.

Returns
  • a NumberFormat for handling Number objects.

public static final NumberFormat getPercentInstance ()

Since: API Level 1

Returns a NumberFormat for formatting and parsing percentage values for the default locale.

Returns
  • a NumberFormat for handling percentage values.

public static NumberFormat getPercentInstance (Locale locale)

Since: API Level 1

Returns a NumberFormat for formatting and parsing percentage values for the specified locale.

Parameters
locale the locale to use.
Returns
  • a NumberFormat for handling percentage values.

public int hashCode ()

Since: API Level 1

Returns an integer hash code for this object. By contract, any two objects for which equals(Object) returns true must return the same hash code value. This means that subclasses of Object usually override both methods or neither method.

Returns
  • this object's hash code.

public boolean isGroupingUsed ()

Since: API Level 1

Indicates whether this number format formats and parses numbers using a grouping separator.

Returns
  • true if a grouping separator is used; false otherwise.

public boolean isParseIntegerOnly ()

Since: API Level 1

Indicates whether this number format only parses integer numbers. Parsing stops if a decimal separator is encountered.

Returns
  • true if this number format only parses integers, false if if parsese integers as well as fractions.

public Number parse (String string)

Since: API Level 1

Parses a Number from the specified string using the rules of this number format.

Parameters
string the string to parse.
Returns
  • the Number resulting from the parsing.
Throws
ParseException if an error occurs during parsing.

public abstract Number parse (String string, ParsePosition position)

Since: API Level 1

Parses a Number from the specified string starting at the index specified by position. If the string is successfully parsed then the index of the ParsePosition is updated to the index following the parsed text. On error, the index is unchanged and the error index of ParsePosition is set to the index where the error occurred.

Parameters
string the string to parse.
position input/output parameter, specifies the start index in string from where to start parsing. If parsing is successful, it is updated with the index following the parsed text; on error, the index is unchanged and the error index is set to the index where the error occurred.
Returns
  • the Number resulting from the parse or null if there is an error.

public final Object parseObject (String string, ParsePosition position)

Since: API Level 1

Parses the specified string starting at the index specified by position. If the string is successfully parsed then the index of the ParsePosition is updated to the index following the parsed text. On error, the index is unchanged and the error index of ParsePosition is set to the index where the error occurred.

Parameters
string the string to parse.
position input/output parameter, specifies the start index in string from where to start parsing. If parsing is successful, it is updated with the index following the parsed text; on error, the index is unchanged and the error index is set to the index where the error occurred.
Returns
  • the object resulting from the parse or null if there is an error.

public void setCurrency (Currency currency)

Since: API Level 1

Sets the currency used by this number format when formatting currency values. The min and max fraction digits remain the same.

This implementation throws UnsupportedOperationException, concrete subclasses should override this method if they support currency formatting.

Parameters
currency the new currency.
Throws
UnsupportedOperationException

public void setGroupingUsed (boolean value)

Since: API Level 1

Sets whether this number format formats and parses numbers using a grouping separator.

Parameters
value true if a grouping separator is used; false otherwise.

public void setMaximumFractionDigits (int value)

Since: API Level 1

Sets the maximum number of fraction digits that are printed when formatting. If the maximum is less than the number of fraction digits, the least significant digits are truncated.

Parameters
value the maximum number of fraction digits.

public void setMaximumIntegerDigits (int value)

Since: API Level 1

Sets the new maximum count of integer digits that are printed when formatting. If the maximum is less than the number of integer digits, the most significant digits are truncated.

Parameters
value the new maximum number of integer numerals for display.

public void setMinimumFractionDigits (int value)

Since: API Level 1

Sets the minimum number of fraction digits that are printed when formatting.

Parameters
value the minimum number of fraction digits.

public void setMinimumIntegerDigits (int value)

Since: API Level 1

Sets the minimum number of integer digits that are printed when formatting.

Parameters
value the minimum number of integer digits.

public void setParseIntegerOnly (boolean value)

Since: API Level 1

Specifies if this number format should parse numbers only as integers or else as any kind of number. If this method is called with a true value then subsequent parsing attempts will stop if a decimal separator is encountered.

Parameters
value true to only parse integers, false to parse integers as well as fractions.