Serializable
, Cloneable
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:
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")}
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 | Description |
---|---|---|
static class |
MessageFormat.Field |
Defines constants that are used as attribute keys in the AttributedCharacterIterator returned from MessageFormat.formatToCharacterIterator . |
Constructor | Description |
---|---|
MessageFormat |
Constructs a MessageFormat for the default FORMAT locale and the specified pattern. |
MessageFormat |
Constructs a MessageFormat for the specified locale and pattern. |
Modifier and Type | Method | Description |
---|---|---|
void |
applyPattern |
Sets the pattern used by this message format. |
Object |
clone() |
Creates and returns a copy of this object. |
boolean |
equals |
Equality comparison between two message format objects |
final StringBuffer |
format |
Formats an array of objects and appends the MessageFormat 's pattern, with format elements replaced by the formatted objects, to the provided StringBuffer . |
final StringBuffer |
format |
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 |
Creates a MessageFormat with the given pattern and uses it to format the given arguments. |
AttributedCharacterIterator |
formatToCharacterIterator |
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 |
Parses text from the beginning of the given string to produce an object array. |
Object[] |
parse |
Parses the string. |
Object |
parseObject |
Parses text from a string to produce an object array. |
void |
setFormat |
Sets the format to use for the format element with the given format element index within the previously set pattern string. |
void |
setFormatByArgumentIndex |
Sets the format to use for the format elements within the previously set pattern string that use the given argument index. |
void |
setFormats |
Sets the formats to use for the format elements in the previously set pattern string. |
void |
setFormatsByArgumentIndex |
Sets the formats to use for the values passed into format methods or returned from parse methods. |
void |
setLocale |
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, parseObject
public MessageFormat(String pattern)
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.pattern
- the pattern for this message formatIllegalArgumentException
- if the pattern is invalidNullPointerException
- if pattern
is null
public MessageFormat(String pattern, Locale locale)
NullPointerException
if locale
is null
either during the creation of the MessageFormat
object or later when format()
is called by a MessageFormat
instance with a null locale and the implementation utilizes a locale-dependent subformat.pattern
- the pattern for this message formatlocale
- the locale for this message formatIllegalArgumentException
- if the pattern is invalidNullPointerException
- if pattern
is null
or locale
is null
and the implementation uses a locale-dependent subformat.public 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 invalidNullPointerException
- if pattern
is null
public 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 + "}" |
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.
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.result
, 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.NullPointerException
- if result
is null
or if the MessageFormat
instance that calls this method has locale set to null, and the implementation uses a locale-dependent subformat.public static String format(String pattern, Object... arguments)
(new MessageFormat
(pattern)).format
(arguments, new StringBuffer(), null).toString()
pattern
- the pattern stringarguments
- object(s) to formatIllegalArgumentException
- 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
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 Format
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.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.NullPointerException
- if result
is null
or if the MessageFormat
instance that calls this method has locale set to null, and the implementation uses a locale-dependent subformat.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 Format
arguments
- 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:
source
- the string to parsepos
- the parse positionNullPointerException
- if pos
is null
for a non-null source
string.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 Format
source
- 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)
public int hashCode()
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