ChoiceFormat

public class ChoiceFormat
extends NumberFormat

java.lang.Object
   ↳ java.text.Format
     ↳ java.text.NumberFormat
       ↳ java.text.ChoiceFormat


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[] dayOfWeekNames = {"Sun","Mon","Tue","Wed","Thur","Fri","Sat"};
 ChoiceFormat form = new ChoiceFormat(limits, dayOfWeekNames);
 ParsePosition status = new ParsePosition(0);
 for (double i = 0.0; i <= 8.0; ++i) {
     status.setIndex(0);
     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}");
 pattform.setFormats(testFormats);
 Object[] testArgs = {null, "ADisk", null};
 for (int i = 0; i < 4; ++i) {
     testArgs[0] = new Integer(i);
     testArgs[2] = testArgs[0];
     System.out.println(pattform.format(testArgs));
 }
 

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.
 

Synchronization

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.

Summary

Inherited constants

Public constructors

ChoiceFormat(String newPattern)

Constructs with limits and corresponding formats based on the pattern.

ChoiceFormat(double[] limits, String[] formats)

Constructs with the limits and the corresponding formats.

Public methods

void applyPattern(String newPattern)

Sets the pattern.

Object clone()

Overrides Cloneable

boolean equals(Object obj)

Equality comparison 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()
double[] getLimits()
int hashCode()

Generates a hash code for the message format object.

static final 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 is true), or the greatest double less than d (if positive is false).

Number parse(String text, ParsePosition status)

Parses a Number from the input text.

static final 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.

Inherited methods

Public constructors

ChoiceFormat

Added in API level 1
public ChoiceFormat (String newPattern)

Constructs with limits and corresponding formats based on the pattern.

Parameters
newPattern String: the new pattern string

Throws
NullPointerException if newPattern is null

ChoiceFormat

Added in API level 1
public ChoiceFormat (double[] limits, 
                String[] formats)

Constructs with the limits and the corresponding formats.

Parameters
limits double: limits in ascending order

formats String: corresponding format strings

Throws
NullPointerException if limits or formats is null

Public methods

applyPattern

Added in API level 1
public void applyPattern (String newPattern)

Sets the pattern.

Parameters
newPattern String: See the class description.

Throws
NullPointerException if newPattern is null

clone

Added in API level 1
public Object clone ()

Overrides Cloneable

Returns
Object a clone of this instance.

equals

Added in API level 1
public boolean equals (Object obj)

Equality comparison between two

Parameters
obj Object: the reference object with which to compare.

Returns
boolean true if this object is the same as the obj argument; false otherwise.

format

Added in API level 1
public StringBuffer format (double number, 
                StringBuffer toAppendTo, 
                FieldPosition status)

Returns pattern with formatted double.

Parameters
number double: number to be formatted and substituted.

toAppendTo StringBuffer: where text is appended.

status FieldPosition: ignore no useful status is returned.

Returns
StringBuffer the formatted StringBuffer

Throws
NullPointerException if toAppendTo is null

format

Added in API level 1
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.

Parameters
number long: the long number to format

toAppendTo StringBuffer: the StringBuffer to which the formatted text is to be appended

status FieldPosition: keeps track on the position of the field within the returned string. For example, for formatting a number 123456789 in Locale.US locale, if the given fieldPosition is NumberFormat#INTEGER_FIELD, the begin index and end index of fieldPosition will be set to 0 and 11, respectively for the output string 123,456,789.

Returns
StringBuffer the formatted StringBuffer

getFormats

Added in API level 1
public Object[] getFormats ()

Returns
Object[] a copy of the String[] array supplied to the constructor or the most recent call to setChoices(double[], java.lang.String[]).

getLimits

Added in API level 1
public double[] getLimits ()

Returns
double[] a copy of the double[] array supplied to the constructor or the most recent call to setChoices(double[], java.lang.String[]).

hashCode

Added in API level 1
public int hashCode ()

Generates a hash code for the message format object.

Returns
int a hash code value for this object.

nextDouble

Added in API level 1
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.

Implementation Note:
Parameters
d double: the reference value

Returns
double the least double value greather than d

nextDouble

Added in API level 1
public static double nextDouble (double d, 
                boolean positive)

Finds the least double greater than d (if positive is true), or the greatest double less than d (if positive is false). If NaN, returns same value.

Implementation Note:
  • This is equivalent to calling positive ? Math.nextUp(d) : Math.nextDown(d)
Parameters
d double: the reference value

positive boolean: true if the least double is desired; false otherwise

Returns
double the least or greater double value

parse

Added in API level 1
public Number parse (String text, 
                ParsePosition status)

Parses a Number from the input text.

Parameters
text String: the source text.

status ParsePosition: 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 occurred, 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.

Returns
Number A Number representing the value of the number parsed.

Throws
NullPointerException if status is null or if text is null and the list of choice strings is not empty.

previousDouble

Added in API level 1
public static final double previousDouble (double d)

Finds the greatest double less than d. If NaN, returns same value.

Implementation Note:
Parameters
d double: the reference value

Returns
double the greatest double value less than d

See also:

setChoices

Added in API level 1
public void setChoices (double[] limits, 
                String[] formats)

Set the choices to be used in formatting.

Parameters
limits double: 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 String: 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.

Throws
NullPointerException if limits or formats is null

toPattern

Added in API level 1
public String toPattern ()

Gets the pattern.

Returns
String the pattern string