[Chapter 16] ChoiceFormat

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| Chapter 16 The java.text Package |

# ChoiceFormat

## Name

ChoiceFormat

## Synopsis

Class Name:

  `java.text.ChoiceFormat`

Superclass:

  `java.text.NumberFormat`

Immediate Subclasses:

  None

Interfaces Implemented:

  None

Availability:

  New as of JDK 1.1

## Description

The `ChoiceFormat` class is a concrete subclass of `NumberFormat` that maps numerical ranges to strings, or formats. `ChoiceFormat` objects are used most often by `MessageFormat` objects to handle plurals, verb agreement, and other such issues.

The ranges in a `ChoiceFormat` are specified as an ascending array of `double` values, where each number is the bottom end of a range. A value is mapped to a format when it falls within the range for that format. If the value does not fall in any of the ranges, it is mapped to the first or the last format, depending on whether the value is too low or too high. For example, consider the following code:

    double[] limits = {1, 10, 100};
    String[] labels = {"small", "medium", "large"}
    ChoiceFormat cf = new ChoiceFormat(limits, labels);

Any number greater than or equal to one and less than 10 is mapped to the format `"small"`. Any number greater than or equal to 10 and less than 100 is mapped to `"medium"`. Numbers greater than or equal to 100 are mapped to `"large"`. Furthermore, numbers less than one are also mapped to `"small"`.

The `nextDouble()` and `previousDouble()` methods can generate `double` values that are higher or lower than other `double` values. These methods provide another way to specify the limits used by a `ChoiceFormat` object.

As shown above, you can create a `ChoiceFormat` object by specifying the limits and formats in two separate arrays. You can also create a `ChoiceFormat` object using a pattern string that specifies the limits and formats. The string is of the form:

    [limit1]#[format1]|[limit2]#[format2]|...

A `<` character can be used in place of the `#` to indicate that the next higher number, as determined by `nextDouble()`, should be used as the limit. The `toPattern()` method can be used to generate the pattern string for an existing `ChoiceFormat` object.

Note that you create `ChoiceFormat` objects directly, rather than through factory methods. This is because `ChoiceFormat` does not implement any locale-specific behavior. To produce properly internationalized output, the formats for a `ChoiceFormat` should come from a `ResourceBundle` instead of being embedded in the code.

## Class Summary

    public class java.text.ChoiceFormat extends java.text.NumberFormat {
      // Constructors
      public ChoiceFormat(String newPattern);
      public ChoiceFormat(double[] limits, String[] formats);
      // Class Methods
      public static final double nextDouble(double d);
      public static double nextDouble(double d, boolean positive);
      public static final double previousDouble(double d);
      // Instance Methods
      public void applyPattern(String newPattern);
      public Object clone();
      public boolean equals(Object obj);
      public StringBuffer format(double number,
                          StringBuffer toAppendTo, FieldPosition status);
      public StringBuffer format(long number,
                          StringBuffer toAppendTo, FieldPosition status);
      public Object[] getFormats();
      public double[] getLimits();
      public int hashCode();
      public Number parse(String text, ParsePosition status);
      public void setChoices(double[] limits, String[] formats);
      public String toPattern();
    }

## Constructors

### ChoiceFormat

#### public ChoiceFormat(String newPattern)

Parameters

  `newPattern`

    The pattern string.

Description

  This constructor creates a `ChoiceFormat` that uses the limits and formats represented by the given pattern string.

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

Parameters

  `limits`

    An array of limits. Each element is the lower end of a range that runs up through, but not including, the next element.

  `formats`

    An array of format strings that correspond to the limit ranges.

Description

  This constructor creates a `ChoiceFormat` that uses the given limits and format strings

## Class Methods

### nextDouble

#### public static final double nextDouble(double d)

Parameters

  `d`

    A `double` value.

Returns

  The least `double` that is greater than `d`.

Description

  This method returns the least `double` greater than `d`. Calling this method is equivalent to `nextDouble(d,` `true)`.

#### public static double nextDouble(double d, boolean positive)

Parameters

  `d`

    A `double` value.

  `positive`

    A `boolean` value that specifies whether to return the next higher or next lower value.

Returns

  If `positive` is `true`, the least `double` that is greater than `d`. If `positive` is `false`, the greatest `double` that is less than `d`.

Description

  This method finds the next higher or next lower `double` value from `d`, depending on the value of `positive`. If `positive` is `true`, the method returns the least `double` greater than `d`. Otherwise, the method returns the greatest `double` less than `d`.

### previousDouble

#### public static final double previousDouble(double d)

Parameters

  `d`

    A `double` value.

Returns

  The greatest `double` that is less than `d`.

Description

  This method returns the greatest `double` less than `d`. Calling this method is equivalent to `nextDouble(d,` `false)`.

## Instance Methods

### applyPattern

#### public void applyPattern(String newPattern)

Parameters

  `newPattern`

    The pattern string.

Description

  This method tells this `ChoiceFormat` to use the limits and formats represented by the given formatting pattern string. Pattern strings for `ChoiceFormat` objects are described above in the class description.

### clone

#### public Object clone()

Returns

  A copy of this `ChoiceFormat`.

Overrides

  `NumberFormat.clone()`

Description

  This method creates a copy of this `ChoiceFormat` and returns it.

### equals

#### public boolean equals(Object obj)

Parameters

  `obj`

    The object to be compared with this object.

Returns

  `true` if the objects are equal; `false` if they are not.

Overrides

  `Format.equals()`

Description

  This method returns `true` if `obj` is an instance of `ChoiceFormat` and is equivalent to this `ChoiceFormat`.

### format

####

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

Parameters

  `number`

    The `double` value to be formatted.

  `toAppendTo`

    A `StringBuffer` on which to append the formatted information.

  `status`

    Ignored.

Returns

  The given `StringBuffer` with the `String` corresponding to the given number appended to it.

Overrides

  `NumberFormat.format(double,` `StringBuffer,` `FieldPosition)`

Description

  This method formats the given number and appends the result to the given `StringBuffer`.

####

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

Parameters

  `number`

    The `long` value to be formatted.

  `toAppendTo`

    A `StringBuffer` on which to append the formatted information.

  `status`

    Ignored.

Returns

  The given `StringBuffer` with the `String` corresponding to the given number appended to it.

Overrides

  `NumberFormat.format(long, StringBuffer, FieldPosition)`

Description

  This method formats the given number and appends the result to the given `StringBuffer`.

### getFormats

#### public Object[] getFormats()

Returns

  An array that contains the format strings.

Description

  This method returns an array containing the current set of format strings.

### getLimits

#### public double[] getLimits()

Returns

  An array that contains the limit values.

Description

  This method returns an array that contains the current set of limits.

### hashCode

#### public int hashCode()

Returns

  A hashcode for this object.

Overrides

  `NumberFormat.hashCode()`

Description

  This method returns a hashcode for this `ChoiceFormat`.

### parse

#### public Number parse(String text, ParsePosition status)

Parameters

  `text`

    The string to be parsed.

  `status`

    A `ParsePosition` object that can specify a position in the string.

Returns

  A `Number` object that encapsulates the value that corresponds to the longest format string that matches the text that starts at the given position. If there is no matching format string, the value `Double.NaN` is returned.

Overrides

  `NumberFormat.parse(String, ParsePosition)`

Description

  This method parses a number from the given string, starting from the given position. The method returns a `Number` object that encapsulates the value that corresponds to the longest format string that matches the text starting at the given position. If there is no matching format string, the method returns the value `Double.NaN`.

  If there is a matching format string, the index value of the given `ParsePosition` object is incremented by the length of that format string.

### setChoices

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

Parameters

  `limits`

    An array of limits. Each element is the lower end of a range that runs up through, but not including, the next element.

  `formats`

    An array of format strings that correspond to the limit ranges.

Description

  This method sets the limits and format strings that this `ChoiceFormat` uses.

### toPattern

#### public String toPattern()

Returns

  The pattern string of this `ChoiceFormat`.

Description

  This method returns a string that represents the limits and format strings of this `ChoiceFormat`. Pattern strings for `ChoiceFormat` objects are described above in the class description.

## Inherited Methods

Method | Inherited From | Method | Inherited From
--- | --- | --- | ---
`finalize()` | `Object` | `format(double)` | `NumberFormat`
`format(long number)` | `NumberFormat` | `format(Object, StringBuffer, FieldPosition)` | `NumberFormat`
`getClass()` | `Object` | `getMaximumFractionDigits()` | `NumberFormat`
`getMaximumIntegerDigits()` | `NumberFormat` | `getMinimumFractionDigits()` | `NumberFormat`
`getMinimumIntegerDigits()` | `NumberFormat` | `isGroupingUsed()` | `NumberFormat`
`isParseIntegerOnly()` | `NumberFormat` | `notify()` | `Object`
`notifyAll()` | `Object` | `parse(String)` | `NumberFormat`
`parseObject(String)` | `Format` | `parseObject(String, ParsePosition)` | `NumberFormat`
`setGroupingUsed(boolean)` | `NumberFormat` | `setMaximumFractionDigits(int)` | `NumberFormat`
`setMaximumIntegerDigits(int)` | `NumberFormat` | `setMinimumFractionDigits(int)` | `NumberFormat`
`setMinimumIntegerDigits(int)` | `NumberFormat` | `setParseIntegerOnly(boolean)` | `NumberFormat`
`toString()` | `Object` | `wait()` | `Object`
`wait(long)` | `Object` | `wait(long, int)` | `Object`

## See Also

`FieldPosition`, `MessageFormat`, `Number`, `NumberFormat`, `ParsePosition`, `ResourceBundle`, `String`, `StringBuffer`

CharacterIterator |  | CollationElementIterator