public class MessageFormat extends Format
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.
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.
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.
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:
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:
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:
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")}
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.
| Modifier and Type | Class and Description |
|---|---|
static class |
MessageFormat.Field
Defines constants that are used as attribute keys in the
AttributedCharacterIterator returned
from MessageFormat.formatToCharacterIterator. |
| Constructor and Description |
|---|
MessageFormat(String pattern)
Constructs a MessageFormat for the default locale and the
specified pattern.
|
MessageFormat(String pattern,
Locale locale)
Constructs a MessageFormat for the specified locale and
pattern.
|
| Modifier and Type | Method and Description |
|---|---|
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
|
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. |
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. |
static String |
format(String pattern,
Object... arguments)
Creates a MessageFormat with the given pattern and uses it
to format the given arguments.
|
AttributedCharacterIterator |
formatToCharacterIterator(Object arguments)
Formats an array of objects and inserts them into the
MessageFormat's pattern, producing an
AttributedCharacterIterator. |
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
format methods or returned from parse
methods. |
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
format methods or returned from parse
methods. |
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.
|
format, parseObjectpublic MessageFormat(String pattern)
pattern - the pattern for this message formatIllegalArgumentException - if the pattern is invalidpublic MessageFormat(String pattern, Locale locale)
pattern - the pattern for this message formatlocale - the locale for this message formatIllegalArgumentException - if the pattern is invalidpublic void setLocale(Locale locale)
applyPattern
and toPattern methods if format elements specify
a format type and therefore have the subformats created in the
applyPattern method, as well as
format and
formatToCharacterIterator methods
if format elements do not specify a format type and therefore have
the subformats created in the formatting methods.
locale - the locale to be used when creating or comparing subformatspublic Locale getLocale()
public void applyPattern(String pattern)
pattern - the pattern for this message formatIllegalArgumentException - if the pattern is invalidpublic String toPattern()
public void setFormatsByArgumentIndex(Format[] newFormats)
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.
newFormats - the new formats to useNullPointerException - if newFormats is nullpublic void setFormats(Format[] newFormats)
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.
newFormats - the new formats to useNullPointerException - if newFormats is nullpublic void setFormatByArgumentIndex(int argumentIndex,
Format newFormat)
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.
argumentIndex - the argument index for which to use the new formatnewFormat - the new format to usepublic void setFormat(int formatElementIndex,
Format newFormat)
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.
formatElementIndex - the index of a format element within the patternnewFormat - the format to use for the specified format elementArrayIndexOutOfBoundsException - if formatElementIndex is equal to or
larger than the number of format elements in the pattern stringpublic Format[] getFormatsByArgumentIndex()
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.
public Format[] getFormats()
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.
public final StringBuffer format(Object[] arguments, StringBuffer result, FieldPosition pos)
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 + "}"
|
| any | null
| "null"
|
instanceof ChoiceFormat
| any | subformat.format(argument).indexOf('{') >= 0 ?
|
!= null
| any | subformat.format(argument)
|
null
| instanceof Number
| NumberFormat.getInstance(getLocale()).format(argument)
|
null
| instanceof Date
| DateFormat.getDateTimeInstance(DateFormat.SHORT, DateFormat.SHORT, getLocale()).format(argument)
|
null
| instanceof String
| argument
|
null
| any | argument.toString()
|
If pos is non-null, and refers to
Field.ARGUMENT, the location of the first formatted
string will be returned.
arguments - an array of objects to be formatted and substituted.result - where text is appended.pos - On input: an alignment field, if desired.
On output: the offsets of the alignment field.IllegalArgumentException - if an argument in the
arguments array is not of the type
expected by the format element(s) that use it.public static String format(String pattern, Object... arguments)
(new MessageFormat(pattern)).format(arguments, new StringBuffer(), null).toString()
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.public final StringBuffer format(Object arguments, StringBuffer result, FieldPosition pos)
MessageFormat's
pattern, with format elements replaced by the formatted objects, to the
provided StringBuffer.
This is equivalent to
format((Object[]) arguments, result, pos)format in class Formatarguments - an array of objects to be formatted and substituted.result - where text is appended.pos - On input: an alignment field, if desired.
On output: the offsets of the alignment field.toAppendTo,
with formatted text appendedIllegalArgumentException - if an argument in the
arguments array is not of the type
expected by the format element(s) that use it.public AttributedCharacterIterator formatToCharacterIterator(Object arguments)
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.
formatToCharacterIterator in class Formatarguments - an array of objects to be formatted and substituted.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.public Object[] parse(String source, ParsePosition pos)
Caveats: The parse may fail in a number of circumstances. For example:
public Object[] parse(String source) throws ParseException
See the parse(String, ParsePosition) method for more information
on message parsing.
source - A String whose beginning should be parsed.Object array parsed from the string.ParseException - if the beginning of the specified string
cannot be parsed.public Object parseObject(String source, ParsePosition pos)
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(String, ParsePosition) method for more information
on message parsing.
parseObject in class Formatsource - A String, part of which should be parsed.pos - A ParsePosition object with index and error
index information as described above.Object array parsed from the string. In case of
error, returns null.NullPointerException - if pos is null.public Object clone()
public boolean equals(Object obj)
equals in class Objectobj - the reference object with which to compare.true if this object is the same as the obj
argument; false otherwise.Object.hashCode(),
HashMappublic int hashCode()
hashCode in class ObjectObject.equals(java.lang.Object),
System.identityHashCode(java.lang.Object)