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);
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 for 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));
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 for 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));
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 = {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.Field
Defines 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 pattern is
null |
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 pattern is
null |
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 pattern is
null |
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 |
true if this object is the same as the obj
argument; false otherwise. |
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 arguments array
is not of the type expected by the format element(s)
that use it. |
NullPointerException |
if pattern is null |
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
arguments array is not of the type
expected by the format element(s) that use it. |
NullPointerException |
if result is null |
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
arguments array is not of the type
expected by the format element(s) that use it. |
NullPointerException |
if result is null |
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 arguments is null. |
IllegalArgumentException |
if an argument in the
arguments array 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 : A String whose beginning should be parsed. |
Returns | |
---|---|
Object[] |
An Object array 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 pos is null
for a non-null source string. |
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 : A String , part of which should be parsed. |
pos |
ParsePosition : A ParsePosition object with index and error
index information as described above. |
Returns | |
---|---|
Object |
An Object array parsed from the string. In case of
error, returns null. |
Throws | |
---|---|
NullPointerException |
if pos is 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 formatElementIndex is 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 newFormats is 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 newFormats is null |
setLocale
public void setLocale (Locale locale)
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 |
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 2023-04-12 UTC.