java.lang.Object java.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.
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()) | |
time | (none) | DateFormat.getTimeInstance(DateFormat.DEFAULT, getLocale()) |
short | DateFormat.getTimeInstance(DateFormat.SHORT, getLocale()) | |
medium | DateFormat.getTimeInstance(DateFormat.DEFAULT, getLocale()) | |
long | DateFormat.getTimeInstance(DateFormat.LONG, getLocale()) | |
full | DateFormat.getTimeInstance(DateFormat.FULL, getLocale()) | |
SubformatPattern | new SimpleDateFormat(subformatPattern, getLocale()) | |
choice | SubformatPattern | new ChoiceFormat(subformatPattern) |
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:
Here are some examples of usage:
The output is:int planetObject[] arguments= 7; String event ={ new Integer(7), new Date(System.currentTimeMillis()),"a disturbance in the Force";Force" };String result = MessageFormat.format( "At {1,time} on {1,date}, there was {2} on planet {0,number,integer}.", planet, new Date(), event);arguments); output: At 12:30 PM on Jul 3, 2053, there was a disturbance in the Force on planet 7.
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:
Example 2:
The output with different values for fileCount: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));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).
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:
get output such as:
The output with different values for fileCount: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};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.
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 specially;
occurences
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
occurences
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.
Nested Class Summary | |
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static class |
MessageFormat.Field
Defines constants that are used as attribute keys in the AttributedCharacterIterator returned from MessageFormat.formatToCharacterIterator. |
Constructor Summary | |
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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
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 |
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format , parseObject |
Methods inherited from class java.lang. Object |
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finalize , getClass , notify , notifyAll , toString , wait , wait , wait |
Constructor Detail |
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public MessageFormat(String pattern)
public MessageFormat(String pattern, Locale locale)
Method Detail |
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public void setLocale(Locale locale)
public Locale getLocale()
public void applyPattern(String pattern)
public String toPattern()
public void setFormatsByArgumentIndex(Format[] newFormats)
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.
public void setFormats(Format[] newFormats)
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.
public void setFormatByArgumentIndex(int argumentIndex, Format newFormat)
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.
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.
public Format[] getFormatsByArgumentIndex()
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)
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 ? (new MessageFormat(subformat.format(argument), getLocale())).format(argument) : subformat.format(argument) |
!= 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.
public static Stringformat(String pattern, Object... arguments)[] arguments)
(new MessageFormat (pattern)). format (arguments, new StringBuffer(), null).toString()
public final StringBuffer format(Object arguments, StringBuffer result, FieldPosition pos)
format ((Object[]) arguments, result, pos)
public AttributedCharacterIterator formatToCharacterIterator(Object arguments)
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.
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.
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.
public Object clone()
public boolean equals(Object obj)
public int hashCode()