MessageFormat

Kotlin |Java

open class MessageFormat : UFormat

kotlin.Any
↳	java.text.Format
	↳	android.icu.text.UFormat
		↳	android.icu.text.MessageFormat

[icu enhancement] ICU's replacement for java.text.MessageFormat. Methods, fields, and other functionality specific to ICU are labeled '[icu]'.

MessageFormat prepares strings for display to users, with optional arguments (variables/placeholders). The arguments can occur in any order, which is necessary for translation into languages with different grammars.

A MessageFormat is constructed from a pattern string with arguments in {curly braces} which will be replaced by formatted values.

MessageFormat differs from the other Format classes in that you create a MessageFormat object with one of its constructors (not with a getInstance style factory method). Factory methods aren't necessary because MessageFormat itself doesn't implement locale-specific behavior. Any locale-specific behavior is defined by the pattern that you provide and the subformats used for inserted arguments.

Arguments can be named (using identifiers) or numbered (using small ASCII-digit integers). Some of the API methods work only with argument numbers and throw an exception if the pattern has named arguments (see usesNamedArguments()).

An argument might not specify any format type. In this case, a Number value is formatted with a default (for the locale) NumberFormat, a Date value is formatted with a default (for the locale) DateFormat, and for any other value its toString() value is used.

An argument might specify a "simple" type for which the specified Format object is created, cached and used.

An argument might have a "complex" type with nested MessageFormat sub-patterns. During formatting, one of these sub-messages is selected according to the argument value and recursively formatted.

After construction, a custom Format object can be set for a top-level argument, overriding the default formatting and parsing behavior for that argument. However, custom formatting can be achieved more simply by writing a typeless argument in the pattern string and supplying it with a preformatted string value.

When formatting, MessageFormat takes a collection of argument values and writes an output string. The argument values may be passed as an array (when the pattern contains only numbered arguments) or as a Map (which works for both named and numbered arguments).

Each argument is matched with one of the input values by array index or map key and formatted according to its pattern specification (or using a custom Format object if one was set). A numbered pattern argument is matched with a map key that contains that number as an ASCII-decimal-digit string (without leading zero).

Patterns and Their Interpretation

MessageFormat uses patterns of the following form:

message = messageText (argument messageText)*
  argument = noneArg | simpleArg | complexArg
  complexArg = choiceArg | pluralArg | selectArg | selectordinalArg
 
  noneArg = '{' argNameOrNumber '}'
  simpleArg = '{' argNameOrNumber ',' argType [',' argStyle] '}'
  choiceArg = '{' argNameOrNumber ',' "choice" ',' choiceStyle '}'
  pluralArg = '{' argNameOrNumber ',' "plural" ',' pluralStyle '}'
  selectArg = '{' argNameOrNumber ',' "select" ',' selectStyle '}'
  selectordinalArg = '{' argNameOrNumber ',' "selectordinal" ',' pluralStyle '}'
 
  choiceStyle: see <code><a docref="java.text.ChoiceFormat">ChoiceFormat</a></code>pluralStyle: see <code><a docref="android.icu.text.PluralFormat">PluralFormat</a></code>selectStyle: see <code><a docref="android.icu.text.SelectFormat">SelectFormat</a></code>argNameOrNumber = argName | argNumber
  argName = [^[[:Pattern_Syntax:][:Pattern_White_Space:]]]+
  argNumber = '0' | ('1'..'9' ('0'..'9')*)
 
  argType = "number" | "date" | "time" | "spellout" | "ordinal" | "duration"
  argStyle = "short" | "medium" | "long" | "full" | "integer" | "currency" | "percent" | argStyleText

messageText can contain quoted literal strings including syntax characters. A quoted literal string begins with an ASCII apostrophe and a syntax character (usually a {curly brace}) and continues until the next single apostrophe. A double ASCII apostrophe inside or outside of a quoted string represents one literal apostrophe.
Quotable syntax characters are the {curly braces} in all messageText parts, plus the '#' sign in a messageText immediately inside a pluralStyle, and the '|' symbol in a messageText immediately inside a choiceStyle.
See also MessagePattern.ApostropheMode
In argStyleText, every single ASCII apostrophe begins and ends quoted literal text, and unquoted {curly braces} must occur in matched pairs.

Recommendation: Use the real apostrophe (single quote) character \\u2019 for human-readable text, and use the ASCII apostrophe (\\u0027 ' ) only in program syntax, like quoting in MessageFormat. See the annotations for U+0027 Apostrophe in The Unicode Standard.

The choice argument type is deprecated. Use plural arguments for proper plural selection, and select arguments for simple selection among a fixed set of choices.

The argType and argStyle values are used to create a Format instance for the format element. The following table shows how the values map to Format instances. Combinations not shown in the table are illegal. Any argStyleText must be a valid pattern string for the Format subclass used.

argType	argStyle	resulting Format object
(none)		`null`
`number`	(none)	`NumberFormat.getInstance(getLocale())`
	`integer`	`NumberFormat.getIntegerInstance(getLocale())`
	`currency`	`NumberFormat.getCurrencyInstance(getLocale())`
	`percent`	`NumberFormat.getPercentInstance(getLocale())`
	argStyleText	`new DecimalFormat(argStyleText, new DecimalFormatSymbols(getLocale()))`
`date`	(none)	`DateFormat.getDateInstance(DateFormat.DEFAULT, getLocale())`
	`short`	`DateFormat.getDateInstance(DateFormat.SHORT, getLocale())`
	`medium`	`DateFormat.getDateInstance(DateFormat.DEFAULT, getLocale())`
	`long`	`DateFormat.getDateInstance(DateFormat.LONG, getLocale())`
	`full`	`DateFormat.getDateInstance(DateFormat.FULL, getLocale())`
	argStyleText	`new SimpleDateFormat(argStyleText, getLocale())`
`time`	(none)	`DateFormat.getTimeInstance(DateFormat.DEFAULT, getLocale())`
	`short`	`DateFormat.getTimeInstance(DateFormat.SHORT, getLocale())`
	`medium`	`DateFormat.getTimeInstance(DateFormat.DEFAULT, getLocale())`
	`long`	`DateFormat.getTimeInstance(DateFormat.LONG, getLocale())`
	`full`	`DateFormat.getTimeInstance(DateFormat.FULL, getLocale())`
	argStyleText	`new SimpleDateFormat(argStyleText, getLocale())`
`spellout`	argStyleText (optional)	`new RuleBasedNumberFormat(getLocale(), RuleBasedNumberFormat.SPELLOUT) .setDefaultRuleset(argStyleText);`
`ordinal`	argStyleText (optional)	`new RuleBasedNumberFormat(getLocale(), RuleBasedNumberFormat.ORDINAL) .setDefaultRuleset(argStyleText);`
`duration`	argStyleText (optional)	`new RuleBasedNumberFormat(getLocale(), RuleBasedNumberFormat.DURATION) .setDefaultRuleset(argStyleText);`

Differences from java.text.MessageFormat

The ICU MessageFormat supports both named and numbered arguments, while the JDK MessageFormat only supports numbered arguments. Named arguments make patterns more readable.

ICU implements a more user-friendly apostrophe quoting syntax. In message text, an apostrophe only begins quoting literal text if it immediately precedes a syntax character (mostly {curly braces}).
In the JDK MessageFormat, an apostrophe always begins quoting, which requires common text like "don't" and "aujourd'hui" to be written with doubled apostrophes like "don''t" and "aujourd''hui". For more details see MessagePattern.ApostropheMode.

ICU does not create a ChoiceFormat object for a choiceArg, pluralArg or selectArg but rather handles such arguments itself. The JDK MessageFormat does create and use a ChoiceFormat object (new ChoiceFormat(argStyleText)). The JDK does not support plural and select arguments at all.

Usage Information

Here are some examples of usage:

Object[] arguments = {
      7,
      new Date(System.currentTimeMillis()),
      "a disturbance in the Force"
  };
 
  String result = MessageFormat.format(
      "At {1,time} on {1,date}, there was {2} on planet {0,number,integer}.",
      arguments);
 
  <em>output</em>: At 12:30 PM on Jul 3, 2053, there was a disturbance
            in the Force on planet 7.

Typically, the message format will come from resources, and the arguments will be dynamically set at runtime.

Example 2:

Object[] testArgs = { 3, "MyDisk" };
 
  MessageFormat form = new MessageFormat(
      "The disk \"{1}\" contains {0} file(s).");
 
  System.out.println(form.format(testArgs));
 
  // output, with different testArgs
  <em>output</em>: The disk "MyDisk" contains 0 file(s).
  <em>output</em>: The disk "MyDisk" contains 1 file(s).
  <em>output</em>: The disk "MyDisk" contains 1,273 file(s).

For messages that include plural forms, you can use a plural argument:

MessageFormat msgFmt = new MessageFormat(
      "{num_files, plural, " +
      "=0{There are no files on disk \"{disk_name}\".}" +
      "=1{There is one file on disk \"{disk_name}\".}" +
      "other{There are # files on disk \"{disk_name}\".}}",
      ULocale.ENGLISH);
  Map args = new HashMap();
  args.put("num_files", 0);
  args.put("disk_name", "MyDisk");
  System.out.println(msgFmt.format(args));
  args.put("num_files", 3);
  System.out.println(msgFmt.format(args));
 
  <em>output</em>:
  There are no files on disk "MyDisk".
  There are 3 files on "MyDisk".

See PluralFormat and PluralRules for details.

Synchronization

MessageFormats 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

Nested classes
open	`Field` Defines constants that are used as attribute keys in the `AttributedCharacterIterator` returned from `MessageFormat.formatToCharacterIterator`.

Public constructors
`MessageFormat(pattern: String!)` Constructs a MessageFormat for the default `FORMAT` locale and the specified pattern.
`MessageFormat(pattern: String!, locale: ULocale!)` Constructs a MessageFormat for the specified locale and pattern.
`MessageFormat(pattern: String!, locale: Locale!)` Constructs a MessageFormat for the specified locale and pattern.

Public methods
open Unit	`applyPattern(pttrn: String!)` Sets the pattern used by this message format.
open Unit	`applyPattern(pattern: String!, aposMode: MessagePattern.ApostropheMode!)` [icu] Sets the ApostropheMode and the pattern used by this message format.
open static String!	`autoQuoteApostrophe(pattern: String!)` [icu] Converts an 'apostrophe-friendly' pattern into a standard pattern.
open Any	`clone()` Creates and returns a copy of this object.
open Boolean	`equals(other: Any?)` Indicates whether some other object is "equal to" this one.
StringBuffer!	`format(arguments: Any!, result: StringBuffer!, pos: FieldPosition!)` Formats a map or array of objects and appends the `MessageFormat`'s pattern, with format elements replaced by the formatted objects, to the provided `StringBuffer`.
StringBuffer!	`format(arguments: Array<Any!>!, result: StringBuffer!, pos: FieldPosition!)` Formats an array of objects and appends the `MessageFormat`'s pattern, with arguments replaced by the formatted objects, to the provided `StringBuffer`.
StringBuffer!	`format(arguments: MutableMap<String!, Any!>!, result: StringBuffer!, pos: FieldPosition!)` Formats a map of objects and appends the `MessageFormat`'s pattern, with arguments replaced by the formatted objects, to the provided `StringBuffer`.
open static String!	`format(pattern: String!, vararg arguments: Any!)` Creates a MessageFormat with the given pattern and uses it to format the given arguments.
open static String!	`format(pattern: String!, arguments: MutableMap<String!, Any!>!)` Creates a MessageFormat with the given pattern and uses it to format the given arguments.
open AttributedCharacterIterator!	`formatToCharacterIterator(arguments: Any!)` Formats an array of objects and inserts them into the `MessageFormat`'s pattern, producing an `AttributedCharacterIterator`.
open MessagePattern.ApostropheMode!	`getApostropheMode()` [icu]
open MutableSet<String!>!	`getArgumentNames()` [icu] Returns the top-level argument names.
open Format!	`getFormatByArgumentName(argumentName: String!)` [icu] Returns the first top-level format associated with the given argument name.
open Array<Format!>!	`getFormats()` Returns the Format objects used for the format elements in the previously set pattern string.
open Array<Format!>!	`getFormatsByArgumentIndex()` Returns the Format objects used for the values passed into `format` methods or returned from `parse` methods.
open Locale!	`getLocale()` Returns the locale that's used when creating or comparing subformats.
open ULocale!	`getULocale()` [icu] Returns the locale that's used when creating argument Format objects.
open Int	`hashCode()` Returns a hash code value for the object.
open Array<Any!>!	`parse(source: String!)` Parses text from the beginning of the given string to produce an object array.
open Array<Any!>!	`parse(source: String!, pos: ParsePosition!)` Parses the string.
open Any!	`parseObject(source: String!, pos: ParsePosition!)` Parses text from a string to produce an object array or Map.
open MutableMap<String!, Any!>!	`parseToMap(source: String!)` [icu] Parses text from the beginning of the given string to produce a map from argument to values.
open MutableMap<String!, Any!>!	`parseToMap(source: String!, pos: ParsePosition!)` [icu] Parses the string, returning the results in a Map.
open Unit	`setFormat(formatElementIndex: Int, newFormat: Format!)` Sets the Format object to use for the format element with the given format element index within the previously set pattern string.
open Unit	`setFormatByArgumentIndex(argumentIndex: Int, newFormat: Format!)` Sets the Format object to use for the format elements within the previously set pattern string that use the given argument index.
open Unit	`setFormatByArgumentName(argumentName: String!, newFormat: Format!)` [icu] Sets the Format object to use for the format elements within the previously set pattern string that use the given argument name.
open Unit	`setFormats(newFormats: Array<Format!>!)` Sets the Format objects to use for the format elements in the previously set pattern string.
open Unit	`setFormatsByArgumentIndex(newFormats: Array<Format!>!)` Sets the Format objects to use for the values passed into `format` methods or returned from `parse` methods.
open Unit	`setFormatsByArgumentName(newFormats: MutableMap<String!, Format!>!)` [icu] Sets the Format objects to use for the values passed into `format` methods or returned from `parse` methods.
open Unit	`setLocale(locale: ULocale!)` Sets the locale to be used for creating argument Format objects.
open Unit	`setLocale(locale: Locale!)` Sets the locale to be used for creating argument Format objects.
open String!	`toPattern()` Returns the applied pattern string.
open Boolean	`usesNamedArguments()` [icu] Returns true if this MessageFormat uses named arguments, and false otherwise.

Parameters
`pattern`	String!: the pattern for this message format
`locale`	ULocale!: the locale for this message format

Parameters
`pattern`	String!: the pattern for this message format
`aposMode`	MessagePattern.ApostropheMode!: the new ApostropheMode

Parameters
`obj`	The object to format
`toAppendTo`	where the text is to be appended
`pos`	FieldPosition!: On input: an alignment field, if desired On output: the offsets of the alignment field
`arguments`	Any!: a map or array of objects to be formatted
`result`	StringBuffer!: where text is appended

Exceptions
`java.lang.NullPointerException`	if `toAppendTo` or `pos` is null
`java.lang.IllegalArgumentException`	if `arguments` is an array of Object and this format uses named arguments

argType or Format	value object	Formatted Text
any	unavailable	`"{" + argNameOrNumber + "}"`
any	`null`	`"null"`
custom Format `!= null`	any	`customFormat.format(argument)`
noneArg, or custom Format `== null`	`instanceof Number`	`NumberFormat.getInstance(getLocale()).format(argument)`
noneArg, or custom Format `== null`	`instanceof Date`	`DateFormat.getDateTimeInstance(DateFormat.SHORT, DateFormat.SHORT, getLocale()).format(argument)`
noneArg, or custom Format `== null`	`instanceof String`	`argument`
noneArg, or custom Format `== null`	any	`argument.toString()`
complexArg	any	result of recursive formatting of a selected sub-message

Parameters
`arguments`	Array<Any!>!: an array of objects to be formatted and substituted.
`result`	StringBuffer!: where text is appended.
`pos`	FieldPosition!: On input: an alignment field, if desired. On output: the offsets of the alignment field.

Parameters
`arguments`	MutableMap<String!, Any!>!: a map of objects to be formatted and substituted.
`result`	StringBuffer!: where text is appended.
`pos`	FieldPosition!: On input: an alignment field, if desired. On output: the offsets of the alignment field.

Exceptions
`java.lang.NullPointerException`	if obj is null.
`java.lang.IllegalArgumentException`	if a value in the `arguments` array is not of the type expected by the corresponding argument or custom Format object.
`java.lang.NullPointerException`	if `arguments` is null.

Exceptions
`java.text.ParseException`	if the beginning of the specified string cannot be parsed.
`java.lang.IllegalArgumentException`	if this format uses named arguments

Parameters
`source`	String!: A `String`, part of which should be parsed.
`pos`	ParsePosition!: A `ParsePosition` object with index and error index information as described above.

Parameters
`source`	String!: the text to parse
`pos`	ParsePosition!: the position at which to start parsing. on return, contains the result of the parse.

Parameters
`formatElementIndex`	Int: the index of a format element within the pattern
`newFormat`	Format!: the format to use for the specified format element

Parameters
`argumentIndex`	Int: the argument index for which to use the new format
`newFormat`	Format!: the new format to use

Parameters
`argumentName`	String!: the name of the argument to change
`newFormat`	Format!: the new format to use

Exceptions
`java.lang.NullPointerException`	if `newFormats` is null
`java.lang.IllegalArgumentException`	if this formatter uses named arguments

MessageFormat

Patterns and Their Interpretation

Differences from java.text.MessageFormat

Usage Information

Synchronization

Summary

Public constructors

MessageFormat

MessageFormat

MessageFormat

Public methods

applyPattern

applyPattern

autoQuoteApostrophe

clone

equals

format

format

format

format

format

formatToCharacterIterator

getApostropheMode

getArgumentNames

getFormatByArgumentName

getFormats

getFormatsByArgumentIndex

getLocale

getULocale

hashCode

parse

parse

parseObject

parseToMap

parseToMap

setFormat

setFormatByArgumentIndex

setFormatByArgumentName

setFormats

setFormatsByArgumentIndex

setFormatsByArgumentName

setLocale

setLocale

toPattern

usesNamedArguments