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JavaTM 2 Platform Std. Ed. v1.4.2

Class ChoiceFormat

  extended byjava.text.Format
      extended byjava.text.NumberFormat
          extended byjava.text.ChoiceFormat
All Implemented Interfaces:
Cloneable, Serializable

public class ChoiceFormat
extends NumberFormat

A ChoiceFormat allows you to attach a format to a range of numbers. It is generally used in a MessageFormat for handling plurals. The choice is specified with an ascending list of doubles, where each item specifies a half-open interval up to the next item:

 X matches j if and only if limit[j] <= X < limit[j+1]
If there is no match, then either the first or last index is used, depending on whether the number (X) is too low or too high. If the limit array is not in ascending order, the results of formatting will be incorrect. ChoiceFormat also accepts \u221E as equivalent to infinity(INF).

Note: ChoiceFormat differs from the other Format classes in that you create a ChoiceFormat object with a constructor (not with a getInstance style factory method). The factory methods aren't necessary because ChoiceFormat doesn't require any complex setup for a given locale. In fact, ChoiceFormat doesn't implement any locale specific behavior.

When creating a ChoiceFormat, you must specify an array of formats and an array of limits. The length of these arrays must be the same. For example,

  • limits = {1,2,3,4,5,6,7}
    formats = {"Sun","Mon","Tue","Wed","Thur","Fri","Sat"}
  • limits = {0, 1, ChoiceFormat.nextDouble(1)}
    formats = {"no files", "one file", "many files"}
    (nextDouble can be used to get the next higher double, to make the half-open interval.)

Here is a simple example that shows formatting and parsing:

 double[] limits = {1,2,3,4,5,6,7};
 String[] monthNames = {"Sun","Mon","Tue","Wed","Thur","Fri","Sat"};
 ChoiceFormat form = new ChoiceFormat(limits, monthNames);
 ParsePosition status = new ParsePosition(0);
 for (double i = 0.0; i <= 8.0; ++i) {
     System.out.println(i + " -> " + form.format(i) + " -> "
                              + form.parse(form.format(i),status));
Here is a more complex example, with a pattern format:
 double[] filelimits = {0,1,2};
 String[] filepart = {"are no files","is one file","are {2} files"};
 ChoiceFormat fileform = new ChoiceFormat(filelimits, filepart);
 Format[] testFormats = {fileform, null, NumberFormat.getInstance()};
 MessageFormat pattform = new MessageFormat("There {0} on {1}");
 Object[] testArgs = {null, "ADisk", null};
 for (int i = 0; i < 4; ++i) {
     testArgs[0] = new Integer(i);
     testArgs[2] = testArgs[0];

Specifying a pattern for ChoiceFormat objects is fairly straightforward. For example:

 ChoiceFormat fmt = new ChoiceFormat(
      "-1#is negative| 0#is zero or fraction | 1#is one |1.0<is 1+ |2#is two |2<is more than 2.");
 System.out.println("Formatter Pattern : " + fmt.toPattern());

 System.out.println("Format with -INF : " + fmt.format(Double.NEGATIVE_INFINITY));
 System.out.println("Format with -1.0 : " + fmt.format(-1.0));
 System.out.println("Format with 0 : " + fmt.format(0));
 System.out.println("Format with 0.9 : " + fmt.format(0.9));
 System.out.println("Format with 1.0 : " + fmt.format(1));
 System.out.println("Format with 1.5 : " + fmt.format(1.5));
 System.out.println("Format with 2 : " + fmt.format(2));
 System.out.println("Format with 2.1 : " + fmt.format(2.1));
 System.out.println("Format with NaN : " + fmt.format(Double.NaN));
 System.out.println("Format with +INF : " + fmt.format(Double.POSITIVE_INFINITY));
And the output result would be like the following:
Format with -INF : is negative Format with -1.0 : is negative Format with 0 : is zero or fraction Format with 0.9 : is zero or fraction Format with 1.0 : is one Format with 1.5 : is 1+ Format with 2 : is two Format with 2.1 : is more than 2. Format with NaN : is negative Format with +INF : is more than 2.


Choice formats are 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.

See Also:
DecimalFormat, MessageFormat, Serialized Form

Nested Class Summary
Nested classes inherited from class java.text.NumberFormat
Field Summary
Fields inherited from class java.text.NumberFormat
Constructor Summary
ChoiceFormat(double[] limits, String[] formats)
          Constructs with the limits and the corresponding formats.
ChoiceFormat(String newPattern)
          Constructs with limits and corresponding formats based on the pattern.
Method Summary
 void applyPattern(String newPattern)
          Sets the pattern.
 Object clone()
          Overrides Cloneable
 boolean equals(Object obj)
          Equality comparision between two
 StringBuffer format(double number, StringBuffer toAppendTo, FieldPosition status)
          Returns pattern with formatted double.
 StringBuffer format(long number, StringBuffer toAppendTo, FieldPosition status)
          Specialization of format.
 Object[] getFormats()
          Get the formats passed in the constructor.
 double[] getLimits()
          Get the limits passed in the constructor.
 int hashCode()
          Generates a hash code for the message format object.
static double nextDouble(double d)
          Finds the least double greater than d.
static double nextDouble(double d, boolean positive)
          Finds the least double greater than d (if positive == true), or the greatest double less than d (if positive == false).
 Number parse(String text, ParsePosition status)
          Parses a Number from the input text.
static double previousDouble(double d)
          Finds the greatest double less than d.
 void setChoices(double[] limits, String[] formats)
          Set the choices to be used in formatting.
 String toPattern()
          Gets the pattern.
Methods inherited from class java.text.NumberFormat
format, format, format, getAvailableLocales, getCurrency, getCurrencyInstance, getCurrencyInstance, getInstance, getInstance, getIntegerInstance, getIntegerInstance, getMaximumFractionDigits, getMaximumIntegerDigits, getMinimumFractionDigits, getMinimumIntegerDigits, getNumberInstance, getNumberInstance, getPercentInstance, getPercentInstance, isGroupingUsed, isParseIntegerOnly, parse, parseObject, setCurrency, setGroupingUsed, setMaximumFractionDigits, setMaximumIntegerDigits, setMinimumFractionDigits, setMinimumIntegerDigits, setParseIntegerOnly
Methods inherited from class java.text.Format
format, formatToCharacterIterator, parseObject
Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail


public ChoiceFormat(String newPattern)
Constructs with limits and corresponding formats based on the pattern.

See Also:


public ChoiceFormat(double[] limits,
                    String[] formats)
Constructs with the limits and the corresponding formats.

See Also:
setChoices(double[], java.lang.String[])
Method Detail


public void applyPattern(String newPattern)
Sets the pattern.

newPattern - See the class description.


public String toPattern()
Gets the pattern.


public void setChoices(double[] limits,
                       String[] formats)
Set the choices to be used in formatting.

limits - contains the top value that you want parsed with that format,and should be in ascending sorted order. When formatting X, the choice will be the i, where limit[i] <= X < limit[i+1]. If the limit array is not in ascending order, the results of formatting will be incorrect.
formats - are the formats you want to use for each limit. They can be either Format objects or Strings. When formatting with object Y, if the object is a NumberFormat, then ((NumberFormat) Y).format(X) is called. Otherwise Y.toString() is called.


public double[] getLimits()
Get the limits passed in the constructor.

the limits.


public Object[] getFormats()
Get the formats passed in the constructor.

the formats.


public StringBuffer format(long number,
                           StringBuffer toAppendTo,
                           FieldPosition status)
Specialization of format. This method really calls format(double, StringBuffer, FieldPosition) thus the range of longs that are supported is only equal to the range that can be stored by double. This will never be a practical limitation.

Specified by:
format in class NumberFormat
See Also:


public StringBuffer format(double number,
                           StringBuffer toAppendTo,
                           FieldPosition status)
Returns pattern with formatted double.

Specified by:
format in class NumberFormat
number - number to be formatted & substituted.
toAppendTo - where text is appended.
status - ignore no useful status is returned.
See Also:


public Number parse(String text,
                    ParsePosition status)
Parses a Number from the input text.

Specified by:
parse in class NumberFormat
text - the source text.
status - an input-output parameter. On input, the status.index field indicates the first character of the source text that should be parsed. On exit, if no error occured, status.index is set to the first unparsed character in the source text. On exit, if an error did occur, status.index is unchanged and status.errorIndex is set to the first index of the character that caused the parse to fail.
A Number representing the value of the number parsed.
See Also:
NumberFormat.isParseIntegerOnly(), Format.parseObject(java.lang.String, java.text.ParsePosition)


public static final double nextDouble(double d)
Finds the least double greater than d. If NaN, returns same value.

Used to make half-open intervals.

See Also:


public static final double previousDouble(double d)
Finds the greatest double less than d. If NaN, returns same value.

See Also:


public Object clone()
Overrides Cloneable

clone in class NumberFormat


public int hashCode()
Generates a hash code for the message format object.

hashCode in class NumberFormat


public boolean equals(Object obj)
Equality comparision between two

equals in class NumberFormat


public static double nextDouble(double d,
                                boolean positive)
Finds the least double greater than d (if positive == true), or the greatest double less than d (if positive == false). If NaN, returns same value. Does not affect floating-point flags, provided these member functions do not: Double.longBitsToDouble(long) Double.doubleToLongBits(double) Double.isNaN(double)

Copyright 2003 Sun Microsystems, Inc. All rights reserved