Class MessageFormat
- All Implemented Interfaces:
- Serializable,- Cloneable
MessageFormat provides a means to produce concatenated
 messages in a language-neutral way. Use this class 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:
 
 MessageFormatPattern:
         String
         MessageFormatPattern FormatElement String
 FormatElement:
         { ArgumentIndex }
         { ArgumentIndex , FormatType }
         { ArgumentIndex , FormatType , FormatStyle }
 FormatType:
         number
         dtf_date
         dtf_time
         dtf_datetime
         pre-defined DateTimeFormatter(s)
         date
         time
         choice
         list
 FormatStyle:
         short
         medium
         long
         full
         integer
         currency
         percent
         compact_short
         compact_long
         or
         unit
         SubformatPattern
 
 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.
 
 Any constructor or method that takes a String pattern parameter will throw an IllegalArgumentException if the
 pattern contains an ArgumentIndex value that is equal to or exceeds an implementation limit.
 
 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. These values
 are case-insensitive when passed to applyPattern(String). Combinations
 not shown in the table are illegal. A SubformatPattern must
 be a valid pattern string for the Format subclass used.
- Implementation Note:
- In the reference implementation, the limit of ArgumentIndexis 10,000.Quoting Rules in PatternsWithin 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 eachFormatsubclass 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.
 Usage InformationThe following example demonstrates a general usage ofMessageFormat. In internationalized programs, the message format pattern and other static strings will likely be obtained from resource bundles.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 GregorianCalendar(2053, Calendar.JULY, 3, 12, 30).getTime(), event);resultreturns the following:At 12:30:00 PM on Jul 3, 2053, there was a disturbance in the Force on planet 7. For more sophisticated patterns, ChoiceFormatcan be used withMessageFormatto produce accurate forms for singular and plural:MessageFormat msgFmt = new MessageFormat("The disk \"{0}\" contains {1,choice,0#no files|1#one file|1< {1,number,integer} files}."); Object[] args = {"MyDisk", fileCount}; String result = msgFmt.format(args);resultwith different values forfileCount, returns the following:The disk "MyDisk" contains no files. The disk "MyDisk" contains one file. The disk "MyDisk" contains 1,273 files. Notes: As seen in the previous snippet, the string produced by a ChoiceFormatinMessageFormatis treated as special; occurrences of '{' are used to indicate subformats, and cause recursion. If aFormatElementis defined in theChoiceFormatpattern, it will only be formatted according to theFormatTypeandFormatStylepattern provided. The associated subformats of the top levelMessageFormatwill not be applied to theFormatElementdefined in theChoiceFormatpattern. If you create both aMessageFormatandChoiceFormatprogrammatically (instead of using the string patterns), then be careful not to produce a format that recurses on itself, which will cause an infinite loop.Formatting Date and TimeMessageFormat provides patterns that support the date/time formatters in thejava.time.formatandjava.textpackages. Consider the following three examples, with a date of 11/16/2023:1) a date FormatTypewith a fullFormatStyle,Object[] arg = {new GregorianCalendar(2023, Calendar.NOVEMBER, 16).getTime()}; var fmt = new MessageFormat("The date was {0,date,full}"); fmt.format(arg); // returns "The date was Thursday, November 16, 2023"2) a dtf_date FormatTypewith a fullFormatStyle,Object[] arg = {LocalDate.of(2023, 11, 16)}; var fmt = new MessageFormat("The date was {0,dtf_date,full}"); fmt.format(arg); // returns "The date was Thursday, November 16, 2023"3) an ISO_LOCAL_DATE FormatType,Object[] arg = {LocalDate.of(2023, 11, 16)}; var fmt = new MessageFormat("The date was {0,ISO_LOCAL_DATE}"); fmt.format(arg); // returns "The date was 2023-11-16"ParsingWhen 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 = {Double.valueOf(3.1415)}; String result = mf.format( objs ); // result now equals "3.14, 3.1" objs = mf.parse(result, new ParsePosition(0)); // objs now equals {Double.valueOf(3.1)}Likewise, parsing with a MessageFormatobject 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)); // objs now equals {new String("z")}SynchronizationMessage 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. 
- Since:
- 1.1
- See Also:
- 
Nested Class SummaryNested ClassesModifier and TypeClassDescriptionstatic classDefines constants that are used as attribute keys in theAttributedCharacterIteratorreturned fromMessageFormat.formatToCharacterIterator.
- 
Constructor SummaryConstructorsConstructorDescriptionMessageFormat(String pattern) Constructs a MessageFormat for the defaultFORMATlocale and the specified pattern.MessageFormat(String pattern, Locale locale) Constructs a MessageFormat for the specified locale and pattern.
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Method SummaryModifier and TypeMethodDescriptionvoidapplyPattern(String pattern) Sets the pattern used by this message format.clone()Creates and returns a copy of this object.booleanCompares the specified object with thisMessageFormatfor equality.final StringBufferformat(Object[] arguments, StringBuffer result, FieldPosition pos) Formats an array of objects and appends theMessageFormat's pattern, with format elements replaced by the formatted objects, to the providedStringBuffer.final StringBufferformat(Object arguments, StringBuffer result, FieldPosition pos) Formats an array of objects and appends theMessageFormat's pattern, with format elements replaced by the formatted objects, to the providedStringBuffer.static StringCreates a MessageFormat with the given pattern and uses it to format the given arguments.formatToCharacterIterator(Object arguments) Formats an array of objects and inserts them into theMessageFormat's pattern, producing anAttributedCharacterIterator.Format[]Gets the formats used for the format elements in the previously set pattern string.Format[]Gets the formats used for the values passed intoformatmethods or returned fromparsemethods.Gets the locale that's used when creating or comparing subformats.inthashCode()Returns the hash code value for thisMessageFormat.Object[]Parses text from the beginning of the given string to produce an object array.Object[]parse(String source, ParsePosition pos) Parses the string.parseObject(String source, ParsePosition pos) Parses text from a string to produce an object array.voidSets the format to use for the format element with the given format element index within the previously set pattern string.voidsetFormatByArgumentIndex(int argumentIndex, Format newFormat) Sets the format to use for the format elements within the previously set pattern string that use the given argument index.voidsetFormats(Format[] newFormats) Sets the formats to use for the format elements in the previously set pattern string.voidsetFormatsByArgumentIndex(Format[] newFormats) Sets the formats to use for the values passed intoformatmethods or returned fromparsemethods.voidSets the locale to be used when creating or comparing subformats.Returns a String pattern adhering to thepatterns sectionthat represents the current state of thisMessageFormat.toString()Returns a string identifying thisMessageFormat, for debugging.Methods declared in class java.text.Formatformat, parseObject
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Constructor Details- 
MessageFormatConstructs a MessageFormat for the defaultFORMATlocale 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- the pattern for this message format
- Throws:
- IllegalArgumentException- if the pattern is invalid
- NullPointerException- if- patternis- null
 
- 
MessageFormatConstructs 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.- Implementation Requirements:
- The default implementation throws a
 NullPointerExceptioniflocaleisnulleither during the creation of theMessageFormatobject or later whenformat()is called by aMessageFormatinstance with a null locale and the implementation utilizes a locale-dependent subformat.
- Parameters:
- pattern- the pattern for this message format
- locale- the locale for this message format
- Throws:
- IllegalArgumentException- if the pattern is invalid
- NullPointerException- if- patternis- nullor- localeis- nulland the implementation uses a locale-dependent subformat.
- Since:
- 1.4
 
 
- 
- 
Method Details- 
setLocaleSets the locale to be used when creating or comparing subformats. This affects subsequent calls- to the applyPatternandtoPatternmethods if format elements specify a format type and therefore have the subformats created in theapplyPatternmethod, as well as
- to the formatandformatToCharacterIteratormethods if format elements do not specify a format type and therefore have the subformats created in the formatting methods.
 - Parameters:
- locale- the locale to be used when creating or comparing subformats
 
- to the 
- 
getLocaleGets the locale that's used when creating or comparing subformats.- Returns:
- the locale used when creating or comparing subformats
 
- 
applyPatternSets 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- the pattern for this message format
- Throws:
- IllegalArgumentException- if the pattern is invalid
- NullPointerException- if- patternis- null
 
- 
toPatternReturns a String pattern adhering to thepatterns sectionthat represents the current state of thisMessageFormat. The string is constructed from internal information and therefore does not necessarily equal the previously applied pattern. The order ofFormatStylematching is not guaranteed. That is, aFormatStyleproduced may not be equivalent to the corresponding style passed, in the instance that multiple styles are equivalent.- Implementation Requirements:
- The implementation in MessageFormatreturns a string that, when passed to aMessageFormat()constructor orapplyPattern(), produces an instance that is semantically equivalent to this instance. If a subformat cannot be converted to a String pattern, theFormatTypeandFormatStylewill be omitted from theFormatElement.
- Returns:
- a String pattern adhering to the patterns sectionthat represents the current state of thisMessageFormat
 
- 
setFormatsByArgumentIndexSets the formats to use for the values passed intoformatmethods or returned fromparsemethods. The indices of elements innewFormatscorrespond to the argument indices used in the previously set pattern string. The order of formats innewFormatsthus corresponds to the order of elements in theargumentsarray passed to theformatmethods or the result array returned by theparsemethods.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.lengthare replaced.- Parameters:
- newFormats- the new formats to use
- Throws:
- NullPointerException- if- newFormatsis null
- Since:
- 1.4
 
- 
setFormatsSets the formats to use for the format elements in the previously set pattern string. The order of formats innewFormatscorresponds 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.lengthformats are replaced.Since the order of format elements in a pattern string often changes during localization, it is generally better to use the setFormatsByArgumentIndexmethod, which assumes an order of formats corresponding to the order of elements in theargumentsarray passed to theformatmethods or the result array returned by theparsemethods.- Parameters:
- newFormats- the new formats to use
- Throws:
- NullPointerException- if- newFormatsis null
 
- 
setFormatByArgumentIndexSets 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 theargumentsarray passed to theformatmethods or the result array returned by theparsemethods.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- the argument index for which to use the new format
- newFormat- the new format to use
- Since:
- 1.4
 
- 
setFormatSets 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 setFormatByArgumentIndexmethod, which accesses format elements based on the argument index they specify.- Parameters:
- formatElementIndex- the index of a format element within the pattern
- newFormat- the format to use for the specified format element
- Throws:
- ArrayIndexOutOfBoundsException- if- formatElementIndexis equal to or larger than the number of format elements in the pattern string
 
- 
getFormatsByArgumentIndexGets the formats used for the values passed intoformatmethods or returned fromparsemethods. 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 theargumentsarray passed to theformatmethods or the result array returned by theparsemethods.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. - Returns:
- the formats used for the arguments within the pattern
- Since:
- 1.4
 
- 
getFormatsGets 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 getFormatsByArgumentIndexmethod, which assumes an order of formats corresponding to the order of elements in theargumentsarray passed to theformatmethods or the result array returned by theparsemethods.- Returns:
- the formats used for the format elements in the pattern
 
- 
formatFormats an array of objects and appends theMessageFormat's pattern, with format elements replaced by the formatted objects, to the providedStringBuffer.The text substituted for the individual format elements is derived from the current subformat of the format element and the argumentselement at the format element's argument index as indicated by the first matching line of the following table. An argument is unavailable ifargumentsisnullor has fewer than argumentIndex+1 elements.Subformat Argument Formatted Text any unavailable "{" + argumentIndex + "}"null"null"instanceof ChoiceFormatany subformat.format(argument).indexOf('{') >= 0 ?
 (new MessageFormat(subformat.format(argument), getLocale())).format(argument) : subformat.format(argument)!= nullany subformat.format(argument)nullinstanceof NumberNumberFormat.getInstance(getLocale()).format(argument)instanceof DateDateFormat.getDateTimeInstance(DateFormat.SHORT, DateFormat.SHORT, getLocale()).format(argument)instanceof Stringargumentany argument.toString()If posis non-null, and refers toField.ARGUMENT, the location of the first formatted string will be returned.- Parameters:
- arguments- an array of objects to be formatted and substituted.
- result- where text is appended.
- pos- keeps track on the position of the first replaced argument in the output string.
- Returns:
- the string buffer passed in as result, with formatted text appended
- Throws:
- IllegalArgumentException- if an argument in the- argumentsarray is not of the type expected by the format element(s) that use it.
- NullPointerException- if- resultis- nullor if the- MessageFormatinstance that calls this method has locale set to null, and the implementation uses a locale-dependent subformat.
 
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formatCreates a MessageFormat with the given pattern and uses it to format the given arguments. This method returns a string that would be equal to the string returned by(newMessageFormat(pattern)).format(arguments, new StringBuffer(), null).toString()- Parameters:
- pattern- the pattern string
- arguments- object(s) to format
- Returns:
- the formatted string
- Throws:
- IllegalArgumentException- if the pattern is invalid, or if an argument in the- argumentsarray is not of the type expected by the format element(s) that use it.
- NullPointerException- if- patternis- null
 
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formatFormats an array of objects and appends theMessageFormat's pattern, with format elements replaced by the formatted objects, to the providedStringBuffer. This is equivalent toformat((Object[]) arguments, result, pos)- Specified by:
- formatin class- Format
- Parameters:
- arguments- an array of objects to be formatted and substituted.
- result- where text is appended.
- pos- keeps track on the position of the first replaced argument in the output string.
- Returns:
- the string buffer passed in as toAppendTo, with formatted text appended
- Throws:
- IllegalArgumentException- if an argument in the- argumentsarray is not of the type expected by the format element(s) that use it.
- NullPointerException- if- resultis- nullor if the- MessageFormatinstance that calls this method has locale set to null, and the implementation uses a locale-dependent subformat.
 
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formatToCharacterIteratorFormats an array of objects and inserts them into theMessageFormat's pattern, producing anAttributedCharacterIterator. You can use the returnedAttributedCharacterIteratorto build the resulting String, as well as to determine information about the resulting String.The text of the returned AttributedCharacterIteratoris the same that would be returned byformat(arguments, new StringBuffer(), null).toString()In addition, the AttributedCharacterIteratorcontains at least attributes indicating where text was generated from an argument in theargumentsarray. The keys of these attributes are of typeMessageFormat.Field, their values areIntegerobjects indicating the index in theargumentsarray of the argument from which the text was generated.The attributes/value from the underlying Formatinstances thatMessageFormatuses will also be placed in the resultingAttributedCharacterIterator. This allows you to not only find where an argument is placed in the resulting String, but also which fields it contains in turn.- Overrides:
- formatToCharacterIteratorin class- Format
- Parameters:
- arguments- an array of objects to be formatted and substituted.
- Returns:
- AttributedCharacterIterator describing the formatted value.
- Throws:
- NullPointerException- if- argumentsis null.
- IllegalArgumentException- if an argument in the- argumentsarray is not of the type expected by the format element(s) that use it.
- Since:
- 1.4
 
- 
parseParses 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.
 - Parameters:
- source- the string to parse
- pos- the parse position
- Returns:
- an array of parsed objects
- Throws:
- NullPointerException- if- posis- nullfor a non-null- sourcestring.
 
- 
parseParses 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(String, ParsePosition)method for more information on message parsing.- Parameters:
- source- A- Stringwhose beginning should be parsed.
- Returns:
- An Objectarray parsed from the string.
- Throws:
- ParseException- if the beginning of the specified string cannot be parsed.
 
- 
parseObjectParses 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 ofposis 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 updatedposcan be used to indicate the starting point for the next call to this method. If an error occurs, then the index ofposis not changed, the error index ofposis set to the index of the character where the error occurred, and null is returned.See the parse(String, ParsePosition)method for more information on message parsing.- Specified by:
- parseObjectin class- Format
- Parameters:
- source- A- String, part of which should be parsed.
- pos- A- ParsePositionobject with index and error index information as described above.
- Returns:
- An Objectarray parsed from the string. In case of error, returns null.
- Throws:
- NullPointerException- if- posis null.
 
- 
clone
- 
equalsCompares the specified object with thisMessageFormatfor equality. Returns true if the object is also aMessageFormatand the two formats would format any value the same.- Overrides:
- equalsin class- Object
- Implementation Requirements:
- This method performs an equality check with a notion of class
 identity based on getClass(), rather thaninstanceof. Therefore, in the equals methods in subclasses, no instance of this class should compare as equal to an instance of a subclass.
- Parameters:
- obj- object to be compared for equality
- Returns:
- trueif the specified object is equal to this- MessageFormat
- See Also:
 
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hashCodepublic int hashCode()Returns the hash code value for thisMessageFormat.- Overrides:
- hashCodein class- Object
- Implementation Requirements:
- This method calculates the hash code value using the value returned by
 toPattern().
- Returns:
- the hash code value for this MessageFormat
- See Also:
 
- 
toString
 
-