MessageFormat
  public
  
  
  
  class
  MessageFormat
  
  
  
  
    extends Format
  
  
  
  
  
  
| java.lang.Object | ||
| ↳ | java.text.Format | |
| ↳ | java.text.MessageFormat | |
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:
 MessageFormatPattern: String MessageFormatPattern FormatElement String FormatElement: { ArgumentIndex } { ArgumentIndex , FormatType } { ArgumentIndex , FormatType , FormatStyle } FormatType: one of number date time choice FormatStyle: short medium long full integer currency percent SubformatPattern
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.
 
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:
 
The output is: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 following example creates a MessageFormat instance that
 can be used repeatedly:
 
The output with different values forint 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));
fileCount:
 
 For more sophisticated patterns, you can use a ChoiceFormat
 to produce correct forms for singular and plural:
 
The output with different values forMessageFormat 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));
fileCount:
 
 You can create the ChoiceFormat programmatically, as in the
 above example, or by using a pattern. See ChoiceFormat
 for more information.
 
form.applyPattern( "There {0,choice,0#are no files|1#is one file|1<are {0,number,integer} files}.");
 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.
See also:
Summary
| Nested classes | ||
|---|---|---|
| 
        
        
        
        
        class | MessageFormat.FieldDefines constants that are used as attribute keys in the
  | |
| Public constructors | |
|---|---|
| 
      MessageFormat(String pattern)
      Constructs a MessageFormat for the default
  | |
| 
      MessageFormat(String pattern, Locale locale)
      Constructs a MessageFormat for the specified locale and pattern. | |
| Public methods | |
|---|---|
| 
        
        
        
        
        
        void | 
      applyPattern(String pattern)
      Sets the pattern used by this message format. | 
| 
        
        
        
        
        
        Object | 
      clone()
      Creates and returns a copy of this object. | 
| 
        
        
        
        
        
        boolean | 
      equals(Object obj)
      Equality comparison between two message format objects | 
| 
        
        
        static
        
        
        String | 
      format(String pattern, Object... arguments)
      Creates a MessageFormat with the given pattern and uses it to format the given arguments. | 
| 
        
        
        
        final
        
        StringBuffer | 
      format(Object[] arguments, StringBuffer result, FieldPosition pos)
      Formats an array of objects and appends the  | 
| 
        
        
        
        final
        
        StringBuffer | 
      format(Object arguments, StringBuffer result, FieldPosition pos)
      Formats an array of objects and appends the  | 
| 
        
        
        
        
        
        AttributedCharacterIterator | 
      formatToCharacterIterator(Object arguments)
      Formats an array of objects and inserts them into the
  | 
| 
        
        
        
        
        
        Format[] | 
      getFormats()
      Gets the formats used for the format elements in the previously set pattern string. | 
| 
        
        
        
        
        
        Format[] | 
      getFormatsByArgumentIndex()
      Gets the formats used for the values passed into
  | 
| 
        
        
        
        
        
        Locale | 
      getLocale()
      Gets the locale that's used when creating or comparing subformats. | 
| 
        
        
        
        
        
        int | 
      hashCode()
      Generates a hash code for the message format object. | 
| 
        
        
        
        
        
        Object[] | 
      parse(String source)
      Parses text from the beginning of the given string to produce an object array. | 
| 
        
        
        
        
        
        Object[] | 
      parse(String source, ParsePosition pos)
      Parses the string. | 
| 
        
        
        
        
        
        Object | 
      parseObject(String source, ParsePosition pos)
      Parses text from a string to produce an object array. | 
| 
        
        
        
        
        
        void | 
      setFormat(int formatElementIndex, Format newFormat)
      Sets the format to use for the format element with the given format element index within the previously set pattern string. | 
| 
        
        
        
        
        
        void | 
      setFormatByArgumentIndex(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. | 
| 
        
        
        
        
        
        void | 
      setFormats(Format[] newFormats)
      Sets the formats to use for the format elements in the previously set pattern string. | 
| 
        
        
        
        
        
        void | 
      setFormatsByArgumentIndex(Format[] newFormats)
      Sets the formats to use for the values passed into
  | 
| 
        
        
        
        
        
        void | 
      setLocale(Locale locale)
      Sets the locale to be used when creating or comparing subformats. | 
| 
        
        
        
        
        
        String | 
      toPattern()
      Returns a pattern representing the current state of the message format. | 
| Inherited methods | |
|---|---|
Public constructors
MessageFormat
public MessageFormat (String pattern)
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 | 
| Throws | |
|---|---|
| IllegalArgumentException | if the pattern is invalid | 
| NullPointerException | if patternisnull | 
MessageFormat
public MessageFormat (String pattern, 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 | 
| Throws | |
|---|---|
| IllegalArgumentException | if the pattern is invalid | 
| NullPointerException | if patternisnull | 
Public methods
applyPattern
public void applyPattern (String pattern)
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 | 
| Throws | |
|---|---|
| IllegalArgumentException | if the pattern is invalid | 
| NullPointerException | if patternisnull | 
clone
public Object clone ()
Creates and returns a copy of this object.
| Returns | |
|---|---|
| Object | a clone of this instance. | 
equals
public boolean equals (Object obj)
Equality comparison between two message format objects
| Parameters | |
|---|---|
| obj | Object: the reference object with which to compare. | 
| Returns | |
|---|---|
| boolean | trueif this object is the same as the obj
          argument;falseotherwise. | 
format
public static String format (String pattern, Object... arguments)
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 | Object: object(s) to format | 
| Returns | |
|---|---|
| String | 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 patternisnull | 
format
public final StringBuffer format (Object[] arguments, StringBuffer result, FieldPosition pos)
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.
 
| Subformat | Argument | Formatted Text | 
|---|---|---|
| any | unavailable | "{" + argumentIndex + "}" | 
| null | "null" | |
| instanceof ChoiceFormat | any | subformat.format(argument).indexOf('{') >= 0 ? | 
| != 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 | Object: 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. | 
| Returns | |
|---|---|
| StringBuffer | 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 resultisnull | 
format
public final StringBuffer format (Object arguments, StringBuffer result, FieldPosition pos)
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 | |
|---|---|
| arguments | Object: 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. | 
| Returns | |
|---|---|
| StringBuffer | 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 resultisnull | 
formatToCharacterIterator
public AttributedCharacterIterator formatToCharacterIterator (Object arguments)
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 | |
|---|---|
| arguments | Object: an array of objects to be formatted and substituted. | 
| Returns | |
|---|---|
| AttributedCharacterIterator | 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. | 
getFormats
public Format[] getFormats ()
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.
| Returns | |
|---|---|
| Format[] | the formats used for the format elements in the pattern | 
getFormatsByArgumentIndex
public Format[] getFormatsByArgumentIndex ()
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.
| Returns | |
|---|---|
| Format[] | the formats used for the arguments within the pattern | 
getLocale
public Locale getLocale ()
Gets the locale that's used when creating or comparing subformats.
| Returns | |
|---|---|
| Locale | the locale used when creating or comparing subformats | 
hashCode
public int hashCode ()
Generates a hash code for the message format object.
| Returns | |
|---|---|
| int | a hash code value for this object. | 
parse
public Object[] parse (String source)
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: AStringwhose beginning should be parsed. | 
| Returns | |
|---|---|
| Object[] | An Objectarray parsed from the string. | 
| Throws | |
|---|---|
| ParseException | if the beginning of the specified string cannot be parsed. | 
parse
public Object[] parse (String source, ParsePosition pos)
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.
| Parameters | |
|---|---|
| source | String: the string to parse | 
| pos | ParsePosition: the parse position | 
| Returns | |
|---|---|
| Object[] | an array of parsed objects | 
| Throws | |
|---|---|
| NullPointerException | if posisnullfor a non-nullsourcestring. | 
parseObject
public Object parseObject (String source, ParsePosition pos)
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: AString, part of which should be parsed. | 
| pos | ParsePosition: AParsePositionobject with index and error
            index information as described above. | 
| Returns | |
|---|---|
| Object | An Objectarray parsed from the string. In case of
         error, returns null. | 
| Throws | |
|---|---|
| NullPointerException | if posis null. | 
setFormat
public void setFormat (int formatElementIndex, 
                Format newFormat)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 | 
| Throws | |
|---|---|
| ArrayIndexOutOfBoundsException | if formatElementIndexis equal to or
            larger than the number of format elements in the pattern string | 
setFormatByArgumentIndex
public void setFormatByArgumentIndex (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.
 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
public void setFormats (Format[] newFormats)
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 | Format: the new formats to use | 
| Throws | |
|---|---|
| NullPointerException | if newFormatsis null | 
setFormatsByArgumentIndex
public void setFormatsByArgumentIndex (Format[] newFormats)
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 | Format: the new formats to use | 
| Throws | |
|---|---|
| NullPointerException | if newFormatsis null | 
setLocale
public void setLocale (Locale locale)
Sets 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 | Locale: the locale to be used when creating or comparing subformats | 
toPattern
public String toPattern ()
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.
| Returns | |
|---|---|
| String | a pattern representing the current state of the message format | 
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Last updated 2025-02-10 UTC.
