Added in API level 1

MessageFormat

open class MessageFormat : Format
kotlin.Any
   ↳ java.text.Format
   ↳ java.text.MessageFormat

provides a means to produce concatenated messages in a language-neutral way. Use this to construct messages displayed for end users.

MessageFormat takes a set of objects, formats them, then inserts the formatted strings into the pattern at the appropriate places.

Note: 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). The 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 as well as the subformats used for inserted arguments.

Patterns and Their Interpretation

MessageFormat uses patterns of the following form: 
<i>MessageFormatPattern:</i><i>String</i><i>MessageFormatPattern</i><i>FormatElement</i><i>String</i><i>FormatElement:</i>{ <i>ArgumentIndex</i>}
          { <i>ArgumentIndex</i>, <i>FormatType</i>}
          { <i>ArgumentIndex</i>, <i>FormatType</i>, <i>FormatStyle</i>}
 
  <i>FormatType: one of </i>number date time choice
 
  <i>FormatStyle:</i>short
          medium
          long
          full
          integer
          currency
          percent
          <i>SubformatPattern</i>

Within a String, a pair of single quotes can be used to quote any arbitrary characters except single quotes. For example, pattern string "'{0}'" represents string "{0}", not a FormatElement. A single quote itself must be represented by doubled single quotes '' throughout a String. For example, pattern string "'{''}'" is interpreted as a sequence of '{ (start of quoting and a left curly brace), '' (a single quote), and }' (a right curly brace and end of quoting), not '{' and '}' (quoted left and right curly braces): representing string "{'}", not "{}".

A SubformatPattern is interpreted by its corresponding subformat, and subformat-dependent pattern rules apply. For example, pattern string "{1,number,$'#',##}" (SubformatPattern with underline) will produce a number format with the pound-sign quoted, with a result such as: "$#31,45". Refer to each Format subclass documentation for details.

Any unmatched quote is treated as closed at the end of the given pattern. For example, pattern string "'{0}" is treated as pattern "'{0}'".

Any curly braces within an unquoted pattern must be balanced. For example, "ab {0} de" and "ab '}' de" are valid patterns, but "ab {0'}' de", "ab } de" and "''{''" are not.

Warning:
The rules for using quotes within message format patterns unfortunately have shown to be somewhat confusing. In particular, it isn't always obvious to localizers whether single quotes need to be doubled or not. Make sure to inform localizers about the rules, and tell them (for example, by using comments in resource bundle source files) which strings will be processed by MessageFormat. Note that localizers may need to use single quotes in translated strings where the original version doesn't have them.

The ArgumentIndex value is a non-negative integer written using the digits '0' through '9', and represents an index into the arguments array passed to the format methods or the result array returned by the parse methods.

The FormatType and FormatStyle 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. A SubformatPattern must be a valid pattern string for the Format subclass used.

Shows how FormatType and FormatStyle values map to Format instances
FormatType FormatStyle Subformat Created
(none) (none) null
number (none) NumberFormat.getInstance(getLocale())
integer NumberFormat.getIntegerInstance(getLocale())
currency NumberFormat.getCurrencyInstance(getLocale())
percent NumberFormat.getPercentInstance(getLocale())
SubformatPattern new DecimalFormat(subformatPattern, DecimalFormatSymbols.getInstance(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())
SubformatPattern new SimpleDateFormat(subformatPattern, 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())
SubformatPattern new SimpleDateFormat(subformatPattern, getLocale())
choice SubformatPattern new ChoiceFormat(subformatPattern)

Usage Information

Here are some examples of usage. In real internationalized programs, the message format pattern and other static strings will, of course, be obtained from resource bundles. Other parameters will be dynamically determined at runtime.

The first example uses the static method MessageFormat.format, which internally creates a MessageFormat for one-time use: 

int planet = 7;
  String event = "a disturbance in the Force";
 
  String result = MessageFormat.format(
      "At {1,time} on {1,date}, there was {2} on planet {0,number,integer}.",
      planet, new Date(), event);
The output is: 
At 12:30 PM on Jul 3, 2053, there was a disturbance in the Force on planet 7.

The following example creates a MessageFormat instance that can be used repeatedly: 

int fileCount = 1273;
  String diskName = "MyDisk";
  Object[] testArgs = {new Long(fileCount), diskName};
 
  MessageFormat form = new MessageFormat(
      "The disk \"{1}\" contains {0} file(s).");
 
  System.out.println(form.format(testArgs));
The output with different values for fileCount: 
The disk "MyDisk" contains 0 file(s).
  The disk "MyDisk" contains 1 file(s).
  The disk "MyDisk" contains 1,273 file(s).

For more sophisticated patterns, you can use a ChoiceFormat to produce correct forms for singular and plural: 

MessageFormat form = new MessageFormat("The disk \"{1}\" contains {0}.");
  double[] filelimits = {0,1,2};
  String[] filepart = {"no files","one file","{0,number} files"};
  ChoiceFormat fileform = new ChoiceFormat(filelimits, filepart);
  form.setFormatByArgumentIndex(0, fileform);
 
  int fileCount = 1273;
  String diskName = "MyDisk";
  Object[] testArgs = {new Long(fileCount), diskName};
 
  System.out.println(form.format(testArgs));
The output with different values for fileCount: 
The disk "MyDisk" contains no files.
  The disk "MyDisk" contains one file.
  The disk "MyDisk" contains 1,273 files.

You can create the ChoiceFormat programmatically, as in the above example, or by using a pattern. See ChoiceFormat for more information. 

<code>form.applyPattern(
     "There {0,choice,0#are no files|1#is one file|1&lt;are {0,number,integer} files}.");
  </code>

Note: As we see above, the string produced by a ChoiceFormat in MessageFormat is treated as special; occurrences of '{' are used to indicate subformats, and cause recursion. If you create both a MessageFormat and ChoiceFormat programmatically (instead of using the string patterns), then be careful not to produce a format that recurses on itself, which will cause an infinite loop.

When a single argument is parsed more than once in the string, the last match will be the final result of the parsing. For example, 

MessageFormat mf = new MessageFormat("{0,number,#.##}, {0,number,#.#}");
  Object[] objs = {new Double(3.1415)};
  String result = mf.format( objs );
  // result now equals "3.14, 3.1"
  objs = null;
  objs = mf.parse(result, new ParsePosition(0));
  // objs now equals {new Double(3.1)}

Likewise, parsing with a MessageFormat object using patterns containing multiple occurrences of the same argument would return the last match. For example, 

MessageFormat mf = new MessageFormat("{0}, {0}, {0}");
  String forParsing = "x, y, z";
  Object[] objs = mf.parse(forParsing, new ParsePosition(0));
  // result now equals {new String("z")}

Synchronization

Message 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

Nested classes
open

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: Locale!)

Constructs a MessageFormat for the specified locale and pattern.
Public methods
open Unit
applyPattern(pattern: String!)

Sets the pattern used by this message format.
open Any

Creates and returns a copy of this object.
open Boolean
equals(other: Any?)

Equality comparison between two message format objects
StringBuffer!
format(arguments: Array<Any!>!, result: StringBuffer!, pos: FieldPosition!)

Formats an array of objects and appends the MessageFormat's pattern, with format elements replaced by the formatted objects, to the provided StringBuffer.
StringBuffer!
format(arguments: Any!, result: StringBuffer!, pos: FieldPosition!)

Formats an array of objects and appends the MessageFormat's pattern, with format elements 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 AttributedCharacterIterator!

Formats an array of objects and inserts them into the MessageFormat's pattern, producing an AttributedCharacterIterator.
open Array<Format!>!

Gets the formats used for the format elements in the previously set pattern string.
open Array<Format!>!

Gets the formats used for the values passed into format methods or returned from parse methods.
open Locale!

Gets the locale that's used when creating or comparing subformats.
open Int

Generates a hash code for the message format object.
open Array<Any!>!
parse(source: String!, pos: ParsePosition!)

Parses the string.
open Array<Any!>!
parse(source: String!)

Parses text from the beginning of the given string to produce an object array.
open Any!
parseObject(source: String!, pos: ParsePosition!)

Parses text from a string to produce an object array.
open Unit
setFormat(formatElementIndex: Int, newFormat: Format!)

Sets the format 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 to use for the format elements within the previously set pattern string that use the given argument index.
open Unit
setFormats(newFormats: Array<Format!>!)

Sets the formats to use for the format elements in the previously set pattern string.
open Unit

Sets the formats to use for the values passed into format methods or returned from parse methods.
open Unit
setLocale(locale: Locale!)

Sets the locale to be used when creating or comparing subformats.
open String!

Returns a pattern representing the current state of the message format.
Inherited functions

Public constructors

MessageFormat

Added in API level 1
MessageFormat(pattern: String!)

Constructs a MessageFormat for the default FORMAT locale and the specified pattern. The constructor first sets the locale, then parses the pattern and creates a list of subformats for the format elements contained in it. Patterns and their interpretation are specified in the class description.

Parameters
pattern String!: the pattern for this message format
Exceptions
java.lang.IllegalArgumentException if the pattern is invalid
java.lang.NullPointerException if pattern is null

MessageFormat

Added in API level 1
MessageFormat(
    pattern: String!, 
    locale: Locale!)

Constructs a MessageFormat for the specified locale and pattern. The constructor first sets the locale, then parses the pattern and creates a list of subformats for the format elements contained in it. Patterns and their interpretation are specified in the class description.

Parameters
pattern String!: the pattern for this message format
locale Locale!: the locale for this message format
Exceptions
java.lang.IllegalArgumentException if the pattern is invalid
java.lang.NullPointerException if pattern is null

Public methods

applyPattern

Added in API level 1
open fun applyPattern(pattern: String!): Unit

Sets the pattern used by this message format. The method parses the pattern and creates a list of subformats for the format elements contained in it. Patterns and their interpretation are specified in the class description.

Parameters
pattern String!: the pattern for this message format
Exceptions
java.lang.IllegalArgumentException if the pattern is invalid
java.lang.NullPointerException if pattern is null

clone

Added in API level 1
open fun clone(): Any

Creates and returns a copy of this object.

Return
Any a clone of this instance.
Exceptions
java.lang.CloneNotSupportedException if the object's class does not support the Cloneable interface. Subclasses that override the clone method can also throw this exception to indicate that an instance cannot be cloned.

equals

Added in API level 1
open fun equals(other: Any?): Boolean

Equality comparison between two message format objects

Parameters
obj the reference object with which to compare.
Return
Boolean true if this object is the same as the obj argument; false otherwise.

format

Added in API level 1
fun format(
    arguments: Array<Any!>!, 
    result: StringBuffer!, 
    pos: FieldPosition!
): StringBuffer!

Formats an array of objects and appends the MessageFormat's pattern, with format elements replaced by the formatted objects, to the provided StringBuffer.

The text substituted for the individual format elements is derived from the current subformat of the format element and the arguments element at the format element's argument index as indicated by the first matching line of the following table. An argument is unavailable if arguments is null or has fewer than argumentIndex+1 elements.

Examples of subformat,argument,and formatted text
Subformat Argument Formatted Text
any unavailable "{" + argumentIndex + "}"
null "null"
instanceof ChoiceFormat any subformat.format(argument).indexOf('{') >= 0 ?
(new MessageFormat(subformat.format(argument), getLocale())).format(argument) : subformat.format(argument)
!= null any subformat.format(argument)
null instanceof Number NumberFormat.getInstance(getLocale()).format(argument)
instanceof Date DateFormat.getDateTimeInstance(DateFormat.SHORT, DateFormat.SHORT, getLocale()).format(argument)
instanceof String argument
any argument.toString()

If pos is non-null, and refers to Field.ARGUMENT, the location of the first formatted string will be returned.

Parameters
arguments Array<Any!>!: an array of objects to be formatted and substituted.
result StringBuffer!: where text is appended.
pos FieldPosition!: keeps track on the position of the first replaced argument in the output string.
Return
StringBuffer! the string buffer passed in as result, with formatted text appended
Exceptions
java.lang.IllegalArgumentException if an argument in the arguments array is not of the type expected by the format element(s) that use it.
java.lang.NullPointerException if result is null

format

Added in API level 1
fun format(
    arguments: Any!, 
    result: StringBuffer!, 
    pos: FieldPosition!
): StringBuffer!

Formats an array of objects and appends the MessageFormat's pattern, with format elements replaced by the formatted objects, to the provided StringBuffer. This is equivalent to format((Object[]) arguments, result, pos)

Parameters
obj The object to format
toAppendTo where the text is to be appended
pos FieldPosition!: keeps track on the position of the first replaced argument in the output string.
arguments Any!: an array of objects to be formatted and substituted.
result StringBuffer!: where text is appended.
Return
StringBuffer! the string buffer passed in as toAppendTo, with formatted text appended
Exceptions
java.lang.NullPointerException if result is null
java.lang.IllegalArgumentException if an argument in the arguments array is not of the type expected by the format element(s) that use it.

format

Added in API level 1
open static fun format(
    pattern: String!, 
    vararg arguments: Any!
): String!

Creates a MessageFormat with the given pattern and uses it to format the given arguments. This is equivalent to (new MessageFormat(pattern)).format(arguments, new StringBuffer(), null).toString()

Parameters
pattern String!: the pattern string
arguments Any!: object(s) to format
Return
String! the formatted string
Exceptions
java.lang.IllegalArgumentException if the pattern is invalid, or if an argument in the arguments array is not of the type expected by the format element(s) that use it.
java.lang.NullPointerException if pattern is null

formatToCharacterIterator

Added in API level 1
open fun formatToCharacterIterator(arguments: Any!): AttributedCharacterIterator!

Formats an array of objects and inserts them into the MessageFormat's pattern, producing an AttributedCharacterIterator. You can use the returned AttributedCharacterIterator to build the resulting String, as well as to determine information about the resulting String.

The text of the returned AttributedCharacterIterator is the same that would be returned by

format(arguments, new StringBuffer(), null).toString()

In addition, the AttributedCharacterIterator contains at least attributes indicating where text was generated from an argument in the arguments array. The keys of these attributes are of type MessageFormat.Field, their values are Integer objects indicating the index in the arguments array of the argument from which the text was generated.

The attributes/value from the underlying Format instances that MessageFormat uses will also be placed in the resulting AttributedCharacterIterator. This allows you to not only find where an argument is placed in the resulting String, but also which fields it contains in turn.

Parameters
obj The object to format
arguments Any!: an array of objects to be formatted and substituted.
Return
AttributedCharacterIterator! AttributedCharacterIterator describing the formatted value.
Exceptions
java.lang.NullPointerException if arguments is null.
java.lang.IllegalArgumentException if an argument in the arguments array is not of the type expected by the format element(s) that use it.

getFormats

Added in API level 1
open fun getFormats(): Array<Format!>!

Gets the formats used for the format elements in the previously set pattern string. The order of formats in the returned array corresponds to the order of format elements in the pattern string.

Since the order of format elements in a pattern string often changes during localization, it's generally better to use the getFormatsByArgumentIndex method, which assumes an order of formats corresponding to the order of elements in the arguments array passed to the format methods or the result array returned by the parse methods.

Return
Array<Format!>! the formats used for the format elements in the pattern

getFormatsByArgumentIndex

Added in API level 1
open fun getFormatsByArgumentIndex(): Array<Format!>!

Gets the formats used for the values passed into format methods or returned from parse methods. The indices of elements in the returned array correspond to the argument indices used in the previously set pattern string. The order of formats in the returned array thus corresponds to the order of elements in the arguments array passed to the format methods or the result array returned by the parse methods.

If an argument index is used for more than one format element in the pattern string, then the format used for the last such format element is returned in the array. If an argument index is not used for any format element in the pattern string, then null is returned in the array.

Return
Array<Format!>! the formats used for the arguments within the pattern

getLocale

Added in API level 1
open fun getLocale(): Locale!

Gets the locale that's used when creating or comparing subformats.

Return
Locale! the locale used when creating or comparing subformats

hashCode

Added in API level 1
open fun hashCode(): Int

Generates a hash code for the message format object.

Return
Int a hash code value for this object.

parse

Added in API level 1
open fun parse(
    source: String!, 
    pos: ParsePosition!
): Array<Any!>!

Parses the string.

Caveats: The parse may fail in a number of circumstances. For example:

  • If one of the arguments does not occur in the pattern.
  • If the format of an argument loses information, such as with a choice format where a large number formats to "many".
  • Does not yet handle recursion (where the substituted strings contain {n} references.)
  • Will not always find a match (or the correct match) if some part of the parse is ambiguous. For example, if the pattern "{1},{2}" is used with the string arguments {"a,b", "c"}, it will format as "a,b,c". When the result is parsed, it will return {"a", "b,c"}.
  • If a single argument is parsed more than once in the string, then the later parse wins.
When the parse fails, use ParsePosition.getErrorIndex() to find out where in the string the parsing failed. The returned error index is the starting offset of the sub-patterns that the string is comparing with. For example, if the parsing string "AAA {0} BBB" is comparing against the pattern "AAD {0} BBB", the error index is 0. When an error occurs, the call to this method will return null. If the source is null, return an empty array.
Parameters
source String!: the string to parse
pos ParsePosition!: the parse position
Return
Array<Any!>! an array of parsed objects
Exceptions
java.lang.NullPointerException if pos is null for a non-null source string.

parse

Added in API level 1
open fun parse(source: String!): Array<Any!>!

Parses text from the beginning of the given string to produce an object array. The method may not use the entire text of the given string.

See the parse(java.lang.String,java.text.ParsePosition) method for more information on message parsing.

Parameters
source String!: A String whose beginning should be parsed.
Return
Array<Any!>! An Object array parsed from the string.
Exceptions
java.text.ParseException if the beginning of the specified string cannot be parsed.

parseObject

Added in API level 1
open fun parseObject(
    source: String!, 
    pos: ParsePosition!
): Any!

Parses text from a string to produce an object array.

The method attempts to parse text starting at the index given by pos. If parsing succeeds, then the index of pos is updated to the index after the last character used (parsing does not necessarily use all characters up to the end of the string), and the parsed object array is returned. The updated pos can be used to indicate the starting point for the next call to this method. If an error occurs, then the index of pos is not changed, the error index of pos is set to the index of the character where the error occurred, and null is returned.

See the parse(java.lang.String,java.text.ParsePosition) method for more information on message parsing.

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.
Return
Any! An Object array parsed from the string. In case of error, returns null.
Exceptions
java.lang.NullPointerException if pos is null.

setFormat

Added in API level 1
open fun setFormat(
    formatElementIndex: Int, 
    newFormat: Format!
): Unit

Sets the format to use for the format element with the given format element index within the previously set pattern string. The format element index is the zero-based number of the format element counting from the start of the pattern string.

Since the order of format elements in a pattern string often changes during localization, it is generally better to use the setFormatByArgumentIndex method, which accesses format elements based on the argument index they specify.

Parameters
formatElementIndex Int: the index of a format element within the pattern
newFormat Format!: the format to use for the specified format element
Exceptions
java.lang.ArrayIndexOutOfBoundsException if formatElementIndex is equal to or larger than the number of format elements in the pattern string

setFormatByArgumentIndex

Added in API level 1
open fun setFormatByArgumentIndex(
    argumentIndex: Int, 
    newFormat: Format!
): Unit

Sets the format to use for the format elements within the previously set pattern string that use the given argument index. The argument index is part of the format element definition and represents an index into the arguments array passed to the format methods or the result array returned by the parse methods.

If the argument index is used for more than one format element in the pattern string, then the new format is used for all such format elements. If the argument index is not used for any format element in the pattern string, then the new format is ignored.

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

setFormats

Added in API level 1
open fun setFormats(newFormats: Array<Format!>!): Unit

Sets the formats to use for the format elements in the previously set pattern string. The order of formats in newFormats corresponds to the order of format elements in the pattern string.

If more formats are provided than needed by the pattern string, the remaining ones are ignored. If fewer formats are provided than needed, then only the first newFormats.length formats are replaced.

Since the order of format elements in a pattern string often changes during localization, it is generally better to use the setFormatsByArgumentIndex method, which assumes an order of formats corresponding to the order of elements in the arguments array passed to the format methods or the result array returned by the parse methods.

Parameters
newFormats Array<Format!>!: the new formats to use
Exceptions
java.lang.NullPointerException if newFormats is null

setFormatsByArgumentIndex

Added in API level 1
open fun setFormatsByArgumentIndex(newFormats: Array<Format!>!): Unit

Sets the formats to use for the values passed into format methods or returned from parse methods. The indices of elements in newFormats correspond to the argument indices used in the previously set pattern string. The order of formats in newFormats thus corresponds to the order of elements in the arguments array passed to the format methods or the result array returned by the parse methods.

If an argument index is used for more than one format element in the pattern string, then the corresponding new format is used for all such format elements. If an argument index is not used for any format element in the pattern string, then the corresponding new format is ignored. If fewer formats are provided than needed, then only the formats for argument indices less than newFormats.length are replaced.

Parameters
newFormats Array<Format!>!: the new formats to use
Exceptions
java.lang.NullPointerException if newFormats is null

setLocale

Added in API level 1
open fun setLocale(locale: Locale!): Unit

Sets the locale to be used when creating or comparing subformats. This affects subsequent calls

  • to the applyPattern and toPattern methods if format elements specify a format type and therefore have the subformats created in the applyPattern method, as well as
  • to the format and formatToCharacterIterator methods if format elements do not specify a format type and therefore have the subformats created in the formatting methods.
Subformats that have already been created are not affected.

Parameters
locale Locale!: the locale to be used when creating or comparing subformats

toPattern

Added in API level 1
open fun toPattern(): String!

Returns a pattern representing the current state of the message format. The string is constructed from internal information and therefore does not necessarily equal the previously applied pattern.

Return
String! a pattern representing the current state of the message format