Package java.text

Class NumberFormat

java.lang.Object
java.text.Format
java.text.NumberFormat
All Implemented Interfaces:
Serializable, Cloneable
Direct Known Subclasses:
ChoiceFormat, DecimalFormat
public abstract class NumberFormat
extends Format
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 default number format. Use getIntegerInstance() to get an integer number format, getCurrencyInstance() to get the currency number format, and getPercentInstance() to get a format for displaying percentages.

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:
DecimalFormat, ChoiceFormat, Serialized Form

  • Field Details

    • INTEGER_FIELD

      public static final int INTEGER_FIELD
      Field constant identifying the integer part of a number.
      See Also:
      Constant Field Values

    • FRACTION_FIELD

      public static final int FRACTION_FIELD
      Field constant identifying the fractional part of a number.
      See Also:
      Constant Field Values

  • Constructor Details

    • NumberFormat

      protected NumberFormat()
      Used by subclasses. This was public in Java 5.

  • Method Details

    • clone

      public Object clone()
      Returns a new NumberFormat with the same properties.
      Overrides:
      clone in class Format
      Returns:
      a shallow copy of this format.
      See Also:
      Cloneable

    • equals

      public boolean equals​(Object object)
      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.
      Overrides:
      equals in class Object
      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:
      hashCode()

    • format

      public final String format​(double value)
      Formats the specified double using the rules of this number format.
      Parameters:
      value - the double to format.
      Returns:
      the formatted string.

    • format

      public 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.

      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.

    • format

      public final String format​(long value)
      Formats the specified long using the rules of this number format.
      Parameters:
      value - the long to format.
      Returns:
      the formatted string.

    • format

      public 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.

      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.

    • format

      public StringBuffer format​(Object object, StringBuffer buffer, FieldPosition field)
      Formats a number into a supplied buffer.

      The number must be a subclass of Number. Instances of Byte, Short, Integer, and Long have Number.longValue invoked, as do instances of BigInteger where BigInteger.bitLength returns less than 64. All other values have Number.doubleValue invoked instead.

      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.

      Specified by:
      format in class Format
      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.

    • getAvailableLocales

      public static Locale[] getAvailableLocales()
      Returns an array of locales for which custom NumberFormat instances are available.

      Note that Android does not support user-supplied locale service providers.

    • getCurrency

      public Currency getCurrency()
      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

    • getCurrencyInstance

      public static final NumberFormat getCurrencyInstance()
      Returns a NumberFormat for formatting and parsing currency values for the user's default locale. See "Be wary of the default locale".
      Returns:
      a NumberFormat for handling currency values.

    • getCurrencyInstance

      public static NumberFormat getCurrencyInstance​(Locale locale)
      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.

    • getIntegerInstance

      public static final NumberFormat getIntegerInstance()
      Returns a NumberFormat for formatting and parsing integers for the user's default locale. See "Be wary of the default locale".
      Returns:
      a NumberFormat for handling integers.

    • getIntegerInstance

      public static NumberFormat getIntegerInstance​(Locale locale)
      Returns a NumberFormat for formatting and parsing integers for the specified locale.
      Parameters:
      locale - the locale to use.
      Returns:
      a NumberFormat for handling integers.

    • getInstance

      public static final NumberFormat getInstance()
      Returns a NumberFormat for formatting and parsing numbers for the default locale.
      Returns:
      a NumberFormat for handling Number objects.

    • getInstance

      public static NumberFormat getInstance​(Locale locale)
      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.

    • getMaximumFractionDigits

      public int getMaximumFractionDigits()
      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.

    • getMaximumIntegerDigits

      public int getMaximumIntegerDigits()
      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.

    • getMinimumFractionDigits

      public int getMinimumFractionDigits()
      Returns the minimum number of fraction digits that are printed when formatting.
      Returns:
      the minimum number of fraction digits.

    • getMinimumIntegerDigits

      public int getMinimumIntegerDigits()
      Returns the minimum number of integer digits that are printed when formatting.
      Returns:
      the minimum number of integer digits.

    • getNumberInstance

      public static final NumberFormat getNumberInstance()
      Returns a NumberFormat for formatting and parsing numbers for the user's default locale. See "Be wary of the default locale".
      Returns:
      a NumberFormat for handling Number objects.

    • getNumberInstance

      public static NumberFormat getNumberInstance​(Locale locale)
      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.

    • getPercentInstance

      public static final NumberFormat getPercentInstance()
      Returns a NumberFormat for formatting and parsing percentage values for the user's default locale. See "Be wary of the default locale".

      The NumberFormat returned by this method should only be used to format floating-point numbers typically between 0 and 1 (with 1 being 100%). A value such as 0.53 will be treated as 53%, but 53.0 (or the integer 53) will be treated as 5,300%, which is rarely what you intended.

    • getPercentInstance

      public static NumberFormat getPercentInstance​(Locale locale)
      Returns a NumberFormat for formatting and parsing percentage values for the given locale.

      The NumberFormat returned by this method should only be used to format floating-point numbers typically between 0 and 1 (with 1 being 100%). A value such as 0.53 will be treated as 53%, but 53.0 (or the integer 53) will be treated as 5,300%, which is rarely what you intended.

    • hashCode

      public int hashCode()
      Description copied from class: Object
      Returns an integer hash code for this object. By contract, any two objects for which Object.equals(java.lang.Object) returns true must return the same hash code value. This means that subclasses of Object usually override both methods or neither method.

      Note that hash values must not change over time unless information used in equals comparisons also changes.

      See Writing a correct hashCode method if you intend implementing your own hashCode method.

      Overrides:
      hashCode in class Object
      Returns:
      this object's hash code.
      See Also:
      Object.equals(java.lang.Object)

    • isGroupingUsed

      public boolean isGroupingUsed()
      Indicates whether this number format formats and parses numbers using a grouping separator.
      Returns:
      true if a grouping separator is used; false otherwise.

    • isParseIntegerOnly

      public boolean isParseIntegerOnly()
      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.

    • parse

      public Number parse​(String string) throws ParseException
      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.

    • parse

      public abstract Number parse​(String string, ParsePosition position)
      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.

    • parseObject

      public final Object parseObject​(String string, ParsePosition position)
      Description copied from class: Format
      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.
      Specified by:
      parseObject in class Format
      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.

    • setCurrency

      public void setCurrency​(Currency currency)
      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

    • setGroupingUsed

      public void setGroupingUsed​(boolean value)
      Sets whether this number format formats and parses numbers using a grouping separator.
      Parameters:
      value - true if a grouping separator is used; false otherwise.

    • setMaximumFractionDigits

      public void setMaximumFractionDigits​(int value)
      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.

    • setMaximumIntegerDigits

      public void setMaximumIntegerDigits​(int value)
      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.

    • setMinimumFractionDigits

      public void setMinimumFractionDigits​(int value)
      Sets the minimum number of fraction digits that are printed when formatting.
      Parameters:
      value - the minimum number of fraction digits.

    • setMinimumIntegerDigits

      public void setMinimumIntegerDigits​(int value)
      Sets the minimum number of integer digits that are printed when formatting.
      Parameters:
      value - the minimum number of integer digits.

    • setParseIntegerOnly

      public void setParseIntegerOnly​(boolean value)
      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.

    • getRoundingMode

      public RoundingMode getRoundingMode()
      Returns the RoundingMode used by this NumberFormat. The default implementation in NumberFormat throws UnsupportedOperationException. Subclasses for which a rounding mode is meaningful are expected to override this method.
      Since:
      1.6

    • setRoundingMode

      public void setRoundingMode​(RoundingMode roundingMode)
      Sets the RoundingMode used by this NumberFormat. The default implementation in NumberFormat throws UnsupportedOperationException. Subclasses for which a rounding mode is meaningful are expected to override this method.
      Since:
      1.6