ChoiceFormat

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[] 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.

Inherited Constant Summary

Public Constructor Summary

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 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.
final 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.
final 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.

Inherited Method Summary

Public Constructors

public ChoiceFormat (String newPattern)

Constructs with limits and corresponding formats based on the pattern.

Parameters
newPattern

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

Constructs with the limits and the corresponding formats.

Parameters
limits
formats

Public Methods

public void applyPattern (String newPattern)

Sets the pattern.

Parameters
newPattern See the class description.

public Object clone ()

Overrides Cloneable

Returns
  • a clone of this instance.

public boolean equals (Object obj)

Equality comparision between two

Parameters
obj the object to compare this instance with.
Returns
  • true if the specified object is equal to this Object; false otherwise.

public StringBuffer format (double number, StringBuffer toAppendTo, FieldPosition status)

Returns pattern with formatted double.

Parameters
number number to be formatted & substituted.
toAppendTo where text is appended.
status ignore no useful status is returned.

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
toAppendTo
status

public Object[] getFormats ()

Get the formats passed in the constructor.

Returns
  • the formats.

public double[] getLimits ()

Get the limits passed in the constructor.

Returns
  • the limits.

public int hashCode ()

Generates a hash code for the message format object.

Returns
  • this object's hash code.

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.

Parameters
d

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)

Parameters
d
positive

public Number parse (String text, ParsePosition status)

Parses a Number from the input text.

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

public static final double previousDouble (double d)

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

Parameters
d

public void setChoices (double[] limits, String[] formats)

Set the choices to be used in formatting.

Parameters
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 String toPattern ()

Gets the pattern.