- All Implemented Interfaces:
Serializable
,Cloneable
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);
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:
The output with different values forint fileCount = 1273; String diskName = "MyDisk"; Object[] testArgs = {Long.valueOf(fileCount), diskName}; MessageFormat form = new MessageFormat( "The disk \"{1}\" contains {0} file(s)."); System.out.println(form.format(testArgs));
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:
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 = {Long.valueOf(fileCount), diskName}; System.out.println(form.format(testArgs));
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.
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 = {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 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)); // objs 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:
-
Nested Class Summary
Modifier and TypeClassDescriptionstatic class
Defines constants that are used as attribute keys in theAttributedCharacterIterator
returned fromMessageFormat.formatToCharacterIterator
. -
Constructor Summary
ConstructorDescriptionMessageFormat
(String pattern) Constructs a MessageFormat for the defaultFORMAT
locale and the specified pattern.MessageFormat
(String pattern, Locale locale) Constructs a MessageFormat for the specified locale and pattern. -
Method Summary
Modifier and TypeMethodDescriptionvoid
applyPattern
(String pattern) Sets the pattern used by this message format.clone()
Creates and returns a copy of this object.boolean
Compares the specified object with thisMessageFormat
for equality.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
.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
.static String
Creates 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 intoformat
methods or returned fromparse
methods.Gets the locale that's used when creating or comparing subformats.int
hashCode()
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.void
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 intoformat
methods or returned fromparse
methods.void
Sets the locale to be used when creating or comparing subformats.Returns a pattern representing the current state of the message format.Methods declared in class java.text.Format
format, parseObject
-
Constructor Details
-
MessageFormat
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 the class description.- Parameters:
pattern
- the pattern for this message format- Throws:
IllegalArgumentException
- if the pattern is invalidNullPointerException
- ifpattern
isnull
-
MessageFormat
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.- Implementation Requirements:
- The default implementation throws a
NullPointerException
iflocale
isnull
either during the creation of theMessageFormat
object or later whenformat()
is called by aMessageFormat
instance with a null locale and the implementation utilizes a locale-dependent subformat. - Parameters:
pattern
- the pattern for this message formatlocale
- the locale for this message format- Throws:
IllegalArgumentException
- if the pattern is invalidNullPointerException
- ifpattern
isnull
orlocale
isnull
and the implementation uses a locale-dependent subformat.- Since:
- 1.4
-
-
Method Details
-
setLocale
Sets the locale to be used when creating or comparing subformats. This affects subsequent calls- to the
applyPattern
andtoPattern
methods if format elements specify a format type and therefore have the subformats created in theapplyPattern
method, as well as - to the
format
andformatToCharacterIterator
methods 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
-
getLocale
Gets the locale that's used when creating or comparing subformats.- Returns:
- the locale used when creating or comparing subformats
-
applyPattern
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
- the pattern for this message format- Throws:
IllegalArgumentException
- if the pattern is invalidNullPointerException
- ifpattern
isnull
-
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
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 than
newFormats.length
are replaced.- Parameters:
newFormats
- the new formats to use- Throws:
NullPointerException
- ifnewFormats
is null- Since:
- 1.4
-
setFormats
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 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 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
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 formatnewFormat
- the new format to use- Since:
- 1.4
-
setFormat
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
- the index of a format element within the patternnewFormat
- 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
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
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 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
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 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 ifarguments
isnull
or has fewer than argumentIndex+1 elements.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 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 thearguments
array is not of the type expected by the format element(s) that use it.NullPointerException
- ifresult
isnull
or if theMessageFormat
instance that calls this method has locale set to null, and the implementation uses a locale-dependent subformat.
-
format
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
- the pattern stringarguments
- 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
Formats 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:
format
in classFormat
- 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 thearguments
array is not of the type expected by the format element(s) that use it.NullPointerException
- ifresult
isnull
or if theMessageFormat
instance that calls this method has locale set to null, and the implementation uses a locale-dependent subformat.
-
formatToCharacterIterator
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 returned
AttributedCharacterIterator
is the same that would be returned byformat
(arguments, new StringBuffer(), null).toString()In addition, the
AttributedCharacterIterator
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 underlying
Format
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 classFormat
- 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
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
- the string to parsepos
- the parse position- Returns:
- an array of parsed objects
- Throws:
NullPointerException
- ifpos
isnull
for a non-nullsource
string.
-
parse
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(String, ParsePosition)
method for more information on message parsing.- Parameters:
source
- AString
whose beginning should be parsed.- Returns:
- An
Object
array parsed from the string. - Throws:
ParseException
- if the beginning of the specified string cannot be parsed.
-
parseObject
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 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 the
parse(String, ParsePosition)
method for more information on message parsing.- Specified by:
parseObject
in classFormat
- Parameters:
source
- AString
, part of which should be parsed.pos
- AParsePosition
object with index and error index information as described above.- Returns:
- An
Object
array parsed from the string. In case of error, returns null. - Throws:
NullPointerException
- ifpos
is null.
-
clone
-
equals
Compares the specified object with thisMessageFormat
for equality. Returns true if the object is also aMessageFormat
and the two formats would format any value the same.- Overrides:
equals
in classObject
- 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:
true
if the specified object is equal to thisMessageFormat
- See Also:
-
hashCode
public int hashCode()Returns the hash code value for thisMessageFormat
.- Overrides:
hashCode
in classObject
- 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:
-