Module java.base
Package java.text

Class MessageFormat

  • All Implemented Interfaces:
    Serializable,Cloneable
    public classMessageFormatextendsFormat
    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 otherFormat classes in that you create aMessageFormat object with one of its constructors (not with agetInstance style factory method). The factory methods aren't necessary becauseMessageFormat 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:StringMessageFormatPatternFormatElementStringFormatElement:         {ArgumentIndex }         {ArgumentIndex ,FormatType }         {ArgumentIndex ,FormatType ,FormatStyle }FormatType: one of         number date time choiceFormatStyle:         short         medium         long         full         integer         currency         percentSubformatPattern

    Within aString, 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 aFormatElement. A single quote itself must be represented by doubled single quotes'' throughout aString. 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"{}".

    ASubformatPattern 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 eachFormat 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 byMessageFormat. Note that localizers may need to use single quotes in translated strings where the original version doesn't have them.

    TheArgumentIndex value is a non-negative integer written using the digits'0' through'9', and represents an index into thearguments array passed to theformat methods or the result array returned by theparse methods.

    TheFormatType andFormatStyle values are used to create aFormat instance for the format element. The following table shows how the values map toFormat instances. Combinations not shown in the table are illegal. ASubformatPattern must be a valid pattern string for theFormat subclass used.

    Shows how FormatType and FormatStyle values map to Format instances
    FormatTypeFormatStyleSubformat Created
    (none)(none)null
    number(none)NumberFormat.getInstance(getLocale())
    integerNumberFormat.getIntegerInstance(getLocale())
    currencyNumberFormat.getCurrencyInstance(getLocale())
    percentNumberFormat.getPercentInstance(getLocale())
    SubformatPatternnewDecimalFormat(subformatPattern,DecimalFormatSymbols.getInstance(getLocale()))
    date(none)DateFormat.getDateInstance(DateFormat.DEFAULT, getLocale())
    shortDateFormat.getDateInstance(DateFormat.SHORT, getLocale())
    mediumDateFormat.getDateInstance(DateFormat.DEFAULT, getLocale())
    longDateFormat.getDateInstance(DateFormat.LONG, getLocale())
    fullDateFormat.getDateInstance(DateFormat.FULL, getLocale())
    SubformatPatternnewSimpleDateFormat(subformatPattern, getLocale())
    time(none)DateFormat.getTimeInstance(DateFormat.DEFAULT, getLocale())
    shortDateFormat.getTimeInstance(DateFormat.SHORT, getLocale())
    mediumDateFormat.getTimeInstance(DateFormat.DEFAULT, getLocale())
    longDateFormat.getTimeInstance(DateFormat.LONG, getLocale())
    fullDateFormat.getTimeInstance(DateFormat.FULL, getLocale())
    SubformatPatternnewSimpleDateFormat(subformatPattern, getLocale())
    choiceSubformatPatternnewChoiceFormat(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 methodMessageFormat.format, which internally creates aMessageFormat 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 aMessageFormat 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 forfileCount:
     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 aChoiceFormat 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 forfileCount:
     The disk "MyDisk" contains no files. The disk "MyDisk" contains one file. The disk "MyDisk" contains 1,273 files.

    You can create theChoiceFormat programmatically, as in the above example, or by using a pattern. SeeChoiceFormat 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 aChoiceFormat inMessageFormat is treated as special; occurrences of '{' are used to indicate subformats, and cause recursion. If you create both aMessageFormat andChoiceFormat 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 aMessageFormat 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.

    Since:
    1.1
    See Also:
    Locale,Format,NumberFormat,DecimalFormat,DecimalFormatSymbols,ChoiceFormat,DateFormat,SimpleDateFormat,Serialized Form

    • Constructor Detail

      • MessageFormat

        public MessageFormat​(String pattern)
        Constructs a MessageFormat for the defaultFORMAT 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 theclass description.
        Parameters:
        pattern - the pattern for this message format
        Throws:
        IllegalArgumentException - if the pattern is invalid
        NullPointerException - ifpattern isnull

      • 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 theclass description.
        Parameters:
        pattern - the pattern for this message format
        locale - the locale for this message format
        Throws:
        IllegalArgumentException - if the pattern is invalid
        NullPointerException - ifpattern isnull
        Since:
        1.4

    • Method Detail

      • setLocale

        public void setLocale​(Locale locale)
        Sets the locale to be used when creating or comparing subformats. This affects subsequent calls
        • to theapplyPattern andtoPattern methods if format elements specify a format type and therefore have the subformats created in theapplyPattern method, as well as
        • to theformat andformatToCharacterIterator 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 - the locale to be used when creating or comparing subformats

      • getLocale

        public Locale getLocale()
        Gets the locale that's used when creating or comparing subformats.
        Returns:
        the locale used when creating or comparing subformats

      • 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 theclass description.
        Parameters:
        pattern - the pattern for this message format
        Throws:
        IllegalArgumentException - if the pattern is invalid
        NullPointerException - ifpattern isnull

      • 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:
        a pattern representing the current state of the message format

      • setFormatsByArgumentIndex

        public void setFormatsByArgumentIndex​(Format[] newFormats)
        Sets the formats to use for the values passed intoformat methods or returned fromparse methods. The indices of elements innewFormats correspond to the argument indices used in the previously set pattern string. The order of formats innewFormats thus corresponds to the order of elements in thearguments array passed to theformat methods or the result array returned by theparse 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 thannewFormats.length are replaced.

        Parameters:
        newFormats - the new formats to use
        Throws:
        NullPointerException - ifnewFormats is null
        Since:
        1.4

      • 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 innewFormats 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 firstnewFormats.length formats are replaced.

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

        Parameters:
        newFormats - the new formats to use
        Throws:
        NullPointerException - ifnewFormats is null

      • 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 thearguments array passed to theformat methods or the result array returned by theparse 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 - the argument index for which to use the new format
        newFormat - the new format to use
        Since:
        1.4

      • 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 thesetFormatByArgumentIndex method, 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 - ifformatElementIndex is equal to or larger than the number of format elements in the pattern string

      • getFormatsByArgumentIndex

        public Format[] getFormatsByArgumentIndex()
        Gets the formats used for the values passed intoformat methods or returned fromparse 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 thearguments array passed to theformat methods or the result array returned by theparse 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:
        the formats used for the arguments within the pattern
        Since:
        1.4

      • 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 thegetFormatsByArgumentIndex method, which assumes an order of formats corresponding to the order of elements in thearguments array passed to theformat methods or the result array returned by theparse methods.

        Returns:
        the formats used for the format elements in the pattern

      • format

        public final StringBuffer format​(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.

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

        Examples of subformat,argument,and formatted text
        SubformatArgumentFormatted Text
        anyunavailable"{" + argumentIndex + "}"
        null"null"
        instanceof ChoiceFormatanysubformat.format(argument).indexOf('{') >= 0 ?
        (new MessageFormat(subformat.format(argument), getLocale())).format(argument) : subformat.format(argument)
        != nullanysubformat.format(argument)
        nullinstanceof NumberNumberFormat.getInstance(getLocale()).format(argument)
        instanceof DateDateFormat.getDateTimeInstance(DateFormat.SHORT, DateFormat.SHORT, getLocale()).format(argument)
        instanceof Stringargument
        anyargument.toString()

        Ifpos is 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 asresult, with formatted text appended
        Throws:
        IllegalArgumentException - if an argument in thearguments array is not of the type expected by the format element(s) that use it.
        NullPointerException - ifresult isnull

      • 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
        (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 thearguments array is not of the type expected by the format element(s) that use it.
        NullPointerException - ifpattern isnull

      • format

        public final StringBuffer format​(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. This is equivalent to
        format((Object[]) arguments, result, pos)
        Specified by:
        format in 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 astoAppendTo, with formatted text appended
        Throws:
        IllegalArgumentException - if an argument in thearguments array is not of the type expected by the format element(s) that use it.
        NullPointerException - ifresult isnull

      • formatToCharacterIterator

        public AttributedCharacterIterator formatToCharacterIterator​(Object arguments)
        Formats an array of objects and inserts them into theMessageFormat's pattern, producing anAttributedCharacterIterator. You can use the returnedAttributedCharacterIterator to build the resulting String, as well as to determine information about the resulting String.

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

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

        In addition, theAttributedCharacterIterator contains at least attributes indicating where text was generated from an argument in thearguments array. The keys of these attributes are of typeMessageFormat.Field, their values areInteger objects indicating the index in thearguments array of the argument from which the text was generated.

        The attributes/value from the underlyingFormat instances thatMessageFormat uses 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:
        formatToCharacterIterator in class Format
        Parameters:
        arguments - an array of objects to be formatted and substituted.
        Returns:
        AttributedCharacterIterator describing the formatted value.
        Throws:
        NullPointerException - ifarguments is null.
        IllegalArgumentException - if an argument in thearguments array is not of the type expected by the format element(s) that use it.
        Since:
        1.4

      • 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.
        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 - the string to parse
        pos - the parse position
        Returns:
        an array of parsed objects
        Throws:
        NullPointerException - ifpos isnull for a non-nullsource string.

      • parse

        public Object[] parse​(String source)               throwsParseException
        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 theparse(String, ParsePosition) method for more information on message parsing.

        Parameters:
        source - AString whose beginning should be parsed.
        Returns:
        AnObject array parsed from the string.
        Throws:
        ParseException - if the beginning of the specified string cannot be parsed.

      • 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 bypos. If parsing succeeds, then the index ofpos 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 updatedpos can be used to indicate the starting point for the next call to this method. If an error occurs, then the index ofpos is not changed, the error index ofpos is set to the index of the character where the error occurred, and null is returned.

        See theparse(String, ParsePosition) method for more information on message parsing.

        Specified by:
        parseObject in class Format
        Parameters:
        source - AString, part of which should be parsed.
        pos - AParsePosition object with index and error index information as described above.
        Returns:
        AnObject array parsed from the string. In case of error, returns null.
        Throws:
        NullPointerException - ifpos is null.

      • clone

        public Object clone()
        Creates and returns a copy of this object.
        Overrides:
        clone in class Format
        Returns:
        a clone of this instance.
        See Also:
        Cloneable

      • equals

        public boolean equals​(Object obj)
        Equality comparison between two message format objects
        Overrides:
        equals in class Object
        Parameters:
        obj - the reference object with which to compare.
        Returns:
        true if this object is the same as the obj argument;false otherwise.
        See Also:
        Object.hashCode(),HashMap