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JavaTM 2 Platform Std. Ed. v1.4.2 |
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java.lang.Objectjava.text.Format
java.text.MessageFormat
MessageFormat provides a means to produce concatenated
messages in 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
String:
StringPartopt
String StringPart
StringPart:
''
' QuotedString '
UnquotedString
SubformatPattern:
SubformatPatternPartopt
SubformatPattern SubformatPatternPart
SubFormatPatternPart:
' QuotedPattern '
UnquotedPattern
Within a String, "''" represents a single
quote. A QuotedString can contain arbitrary characters
except single quotes; the surrounding single quotes are removed.
An UnquotedString can contain arbitrary characters
except single quotes and left curly brackets. Thus, a string that
should result in the formatted message "'{0}'" can be written as
"'''{'0}''" or "'''{0}'''".
Within a SubformatPattern, different rules apply.
A QuotedPattern can contain arbitrary characters
except single quotes; but the surrounding single quotes are
not removed, so they may be interpreted by the
subformat. For example, "{1,number,$'#',##}" will
produce a number format with the pound-sign quoted, with a result
such as: "$#31,45".
An UnquotedPattern can contain arbitrary characters
except single quotes, but curly braces within it must be balanced.
For example, "ab {0} de" and "ab '}' de"
are valid subformat patterns, but "ab {0'}' de" and
"ab } de" are not.
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.
| Format Type | Format Style | Subformat Created | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| (none) | (none) | null
| |||||||||||||||
number
| (none) | NumberFormat.getInstance(getLocale())
| |||||||||||||||
integer
| NumberFormat.getIntegerInstance(getLocale())
| ||||||||||||||||
currency
| NumberFormat.getCurrencyInstance(getLocale())
| ||||||||||||||||
percent
| NumberFormat.getPercentInstance(getLocale())
| ||||||||||||||||
| SubformatPattern | new DecimalFormat(subformatPattern, new DecimalFormatSymbols(getLocale()))
| ||||||||||||||||
date
| (none) | DateFormat.getDateInstance(DateFormat.DEFAULT, getLocale())
| |||||||||||||||
short
| DateFormat.getDateInstance(DateFormat.SHORT, getLocale())
| ||||||||||||||||
medium
| DateFormat.getDateInstance(DateFormat.DEFAULT, getLocale())
| ||||||||||||||||
long
| DateFormat.getDateInstance(DateFormat.LONG, getLocale())
| ||||||||||||||||
full
| DateFormat.getDateInstance(DateFormat.FULL, getLocale())
| ||||||||||||||||
| SubformatPattern | new SimpleDateFormat(subformatPattern, getLocale())
|
Here are some examples of usage:
Object[] arguments = {
new Integer(7),
new Date(System.currentTimeMillis()),
"a disturbance in the Force"
};
String result = MessageFormat.format(
"At {1,time} on {1,date}, there was {2} on planet {0,number,integer}.",
arguments);
output: At 12:30 PM on Jul 3, 2053, there was a disturbance
in the Force on planet 7.
Typically, the message format will come from resources, and the
arguments will be dynamically set at runtime.
Example 2:
Object[] testArgs = {new Long(3), "MyDisk"};
MessageFormat form = new MessageFormat(
"The disk \"{1}\" contains {0} file(s).");
System.out.println(form.format(testArgs));
// output, with different testArgs
output: The disk "MyDisk" contains 0 file(s).
output: The disk "MyDisk" contains 1 file(s).
output: The disk "MyDisk" contains 1,273 file(s).
For more sophisticated patterns, you can use a ChoiceFormat to get
output such as:
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);
Object[] testArgs = {new Long(12373), "MyDisk"};
System.out.println(form.format(testArgs));
// output, with different testArgs
output: The disk "MyDisk" contains no files.
output: The disk "MyDisk" contains one file.
output: The disk "MyDisk" contains 1,273 files.
You can either do this programmatically, as in the above example,
or by using a pattern (see
ChoiceFormat
for more information) as in:
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 specially;
occurances of '{' are used to indicated 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 occurances 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.
Locale,
Format,
NumberFormat,
DecimalFormat,
ChoiceFormat,
Serialized Form| Nested Class Summary | |
static class |
MessageFormat.Field
Defines constants that are used as attribute keys in the AttributedCharacterIterator returned
from MessageFormat.formatToCharacterIterator. |
| Constructor Summary | |
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. |
|
| Method Summary | |
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. |
| Methods inherited from class java.text.Format |
format, parseObject |
| Methods inherited from class java.lang.Object |
finalize, getClass, notify, notifyAll, toString, wait, wait, wait |
| Constructor Detail |
public MessageFormat(String pattern)
pattern - the pattern for this message format
IllegalArgumentException - if the pattern is invalid
public MessageFormat(String pattern,
Locale locale)
pattern - the pattern for this message formatlocale - the locale for this message format
IllegalArgumentException - if the pattern is invalid| Method Detail |
public void setLocale(Locale locale)
applyPattern
and toPattern methods as well as to the
format and
formatToCharacterIterator 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 format
IllegalArgumentException - 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 use
NullPointerException - 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 use
NullPointerException - if newFormats is null
public 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 use
public 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 element
ArrayIndexOutOfBoundsException - 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 appended
IllegalArgumentException - 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()
clone in class Formatpublic 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(),
Hashtablepublic int hashCode()
hashCode in class ObjectObject.equals(java.lang.Object),
Hashtable
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JavaTM 2 Platform Std. Ed. v1.4.2 |
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Copyright 2003 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.