ChoiceFormat (Java Platform SE 8 )
Keywords: java.text.ChoiceFormat class
Date: 2015-11-19

compact1, compact2, compact3
java.text

## Class ChoiceFormat

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

- All Implemented Interfaces:
    Serializable, Cloneable

      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.

  See Also:
    `DecimalFormat`, `MessageFormat`, Serialized Form

- - ### Nested Class Summary

    - ### Nested classes/interfaces inherited from class java.text.NumberFormat

      `NumberFormat.Field`

  - ### Field Summary

    - ### Fields inherited from class java.text.NumberFormat

      `FRACTION_FIELD, INTEGER_FIELD`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `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

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `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` 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 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, getRoundingMode, isGroupingUsed, isParseIntegerOnly, parse, parseObject, setCurrency, setGroupingUsed, setMaximumFractionDigits, setMaximumIntegerDigits, setMinimumFractionDigits, setMinimumIntegerDigits, setParseIntegerOnly, setRoundingMode`

    - ### 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

    - #### ChoiceFormat

          public ChoiceFormat(String newPattern)

      Constructs with limits and corresponding formats based on the pattern.
      Parameters:
        `newPattern` - the new pattern string
      See Also:
        `applyPattern(java.lang.String)`

    - #### ChoiceFormat

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

      Constructs with the limits and the corresponding formats.
      Parameters:
        `limits` - limits in ascending order
        `formats` - corresponding format strings
      See Also:
        `setChoices(double[], java.lang.String[])`

  - ### Method Detail

    - #### applyPattern

          public void applyPattern(String newPattern)

      Sets the pattern.
      Parameters:
        `newPattern` - See the class description.

    - #### toPattern

          public String toPattern()

      Gets the pattern.
      Returns:
        the pattern string

    - #### setChoices

          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.

    - #### getLimits

          public double[] getLimits()

      Get the limits passed in the constructor.
      Returns:
        the limits.

    - #### getFormats

          public Object[] getFormats()

      Get the formats passed in the constructor.
      Returns:
        the formats.

    - #### format

          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`
      Parameters:
        `number` - the long number to format
        `toAppendTo` - the StringBuffer to which the formatted text is to be appended
        `status` - the field position
      Returns:
        the formatted StringBuffer
      See Also:
        `Format.format(java.lang.Object)`

    - #### format

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

      Returns pattern with formatted double.
      Specified by:
        `format` in class `NumberFormat`
      Parameters:
        `number` - number to be formatted and substituted.
        `toAppendTo` - where text is appended.
        `status` - ignore no useful status is returned.
      Returns:
        the formatted StringBuffer
      See Also:
        `Format.format(java.lang.Object)`

    - #### parse

          public Number parse(String text,
                              ParsePosition status)

      Parses a Number from the input text.
      Specified by:
        `parse` in class `NumberFormat`
      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 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:
        A Number representing the value of the number parsed.
      See Also:
        `NumberFormat.isParseIntegerOnly()`, `Format.parseObject(java.lang.String, java.text.ParsePosition)`

    - #### nextDouble

          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` - the reference value
      Returns:
        the least double value greather than `d`
      See Also:
        `previousDouble(double)`

    - #### previousDouble

          public static final double previousDouble(double d)

      Finds the greatest double less than `d`. If `NaN`, returns same value.
      Parameters:
        `d` - the reference value
      Returns:
        the greatest double value less than `d`
      See Also:
        `nextDouble(double)`

    - #### clone

          public Object clone()

      Overrides Cloneable
      Overrides:
        `clone` in class `NumberFormat`
      Returns:
        a clone of this instance.
      See Also:
        `Cloneable`

    - #### hashCode

          public int hashCode()

      Generates a hash code for the message format object.
      Overrides:
        `hashCode` in class `NumberFormat`
      Returns:
        a hash code value for this object.
      See Also:
        `Object.equals(java.lang.Object)`, `System.identityHashCode(java.lang.Object)`

    - #### equals

          public boolean equals(Object obj)

      Equality comparision between two
      Overrides:
        `equals` in class `NumberFormat`
      Parameters:
        `obj` - the reference object with which to compare.
      Returns:
        `true` if this object is the same as the obj argument; `false` otherwise.
      See Also:
        `Object.hashCode()`, `HashMap`

    - #### nextDouble

          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. Does not affect floating-point flags, provided these member functions do not: Double.longBitsToDouble(long) Double.doubleToLongBits(double) Double.isNaN(double)
      Parameters:
        `d` - the reference value
        `positive` - `true` if the least double is desired; `false` otherwise
      Returns:
        the least or greater double value

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