Class MessageFormat
- java.lang.Object
-
- java.text.Format
-
- java.text.MessageFormat
- All Implemented Interfaces:
-
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.
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:
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);The output is:
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));The output with different values for
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));The output with different values for
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.
- Since:
- 1.1
- See Also:
-
Locale
,Format
,NumberFormat
,DecimalFormat
,DecimalFormatSymbols
,ChoiceFormat
,DateFormat
,SimpleDateFormat
, Serialized Form
Nested Class Summary
Modifier and Type | Class | Description |
---|---|---|
static class | MessageFormat.Field | Defines constants that are used as attribute keys in the |
Constructor Summary
Constructor | Description |
---|---|
MessageFormat(String pattern) | Constructs a MessageFormat for the default |
MessageFormat(String pattern,
Locale locale) | Constructs a MessageFormat for the specified locale and pattern. |
Method Summary
Modifier and Type | Method | 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 |
StringBuffer | format(Object arguments,
StringBuffer result,
FieldPosition pos) | Formats an array of objects and appends the |
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 |
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. |
Methods declared in class java.text.Format
format, parseObject
Methods declared in class java.lang.Object
finalize, getClass, notify, notifyAll, toString, wait, wait, wait
Constructor Detail
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
- the pattern for this message format - Throws:
-
IllegalArgumentException
- if the pattern is invalid -
NullPointerException
- ifpattern
isnull
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
- the pattern for this message format -
locale
- the locale for this message format - Throws:
-
IllegalArgumentException
- if the pattern is invalid -
NullPointerException
- ifpattern
isnull
- Since:
- 1.4
Method Detail
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
- the locale to be used when creating or comparing subformats
getLocale
public Locale getLocale()
Gets the locale that's used when creating or comparing subformats.
- Returns:
- the locale used when creating or comparing subformats
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
- the pattern for this message format - Throws:
-
IllegalArgumentException
- if the pattern is invalid -
NullPointerException
- ifpattern
isnull
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:
- a pattern representing the current state of the message format
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
- the new formats to use - Throws:
-
NullPointerException
- ifnewFormats
is null - Since:
- 1.4
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
- the new formats to use - Throws:
-
NullPointerException
- ifnewFormats
is null
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
- the argument index for which to use the new format -
newFormat
- the new format to use - Since:
- 1.4
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
- the index of a format element within the pattern -
newFormat
- the format to use for the specified format element - Throws:
-
ArrayIndexOutOfBoundsException
- ifformatElementIndex
is equal to or larger than the number of format elements in the pattern string
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:
- the formats used for the arguments within the pattern
- Since:
- 1.4
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:
- the formats used for the format elements in the pattern
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
- 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. - Returns:
- the string buffer passed in as
result
, with formatted text appended - Throws:
-
IllegalArgumentException
- if an argument in thearguments
array is not of the type expected by the format element(s) that use it. -
NullPointerException
- ifresult
isnull
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
- the pattern string -
arguments
- object(s) to format - Returns:
- the formatted string
- Throws:
-
IllegalArgumentException
- if the pattern is invalid, or if an argument in thearguments
array is not of the type expected by the format element(s) that use it. -
NullPointerException
- ifpattern
isnull
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)
- Specified by:
-
format
in classFormat
- Parameters:
-
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. - Returns:
- the string buffer passed in as
toAppendTo
, with formatted text appended - Throws:
-
IllegalArgumentException
- if an argument in thearguments
array is not of the type expected by the format element(s) that use it. -
NullPointerException
- ifresult
isnull
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.
- Overrides:
-
formatToCharacterIterator
in classFormat
- Parameters:
-
arguments
- an array of objects to be formatted and substituted. - Returns:
- AttributedCharacterIterator describing the formatted value.
- Throws:
-
NullPointerException
- ifarguments
is null. -
IllegalArgumentException
- if an argument in thearguments
array is not of the type expected by the format element(s) that use it. - Since:
- 1.4
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
- the string to parse -
pos
- the parse position - Returns:
- an array of parsed objects
- Throws:
-
NullPointerException
- ifpos
isnull
for a non-nullsource
string.
parse
public Object[] parse(String source) throws ParseException
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(String, ParsePosition)
method for more information on message parsing.
- Parameters:
-
source
- AString
whose beginning should be parsed. - Returns:
- An
Object
array parsed from the string. - Throws:
-
ParseException
- if the beginning of the specified string cannot be parsed.
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(String, ParsePosition)
method for more information on message parsing.
- Specified by:
-
parseObject
in classFormat
- Parameters:
-
source
- AString
, part of which should be parsed. -
pos
- AParsePosition
object with index and error index information as described above. - Returns:
- An
Object
array parsed from the string. In case of error, returns null. - Throws:
-
NullPointerException
- ifpos
is null.
clone
public Object clone()
Creates and returns a copy of this object.
equals
public boolean equals(Object obj)
Equality comparison between two message format objects
- Overrides:
-
equals
in classObject
- Parameters:
-
obj
- the reference object with which to compare. - Returns:
-
true
if this object is the same as the obj argument;false
otherwise. - See Also:
-
Object.hashCode()
,HashMap
hashCode
public int hashCode()
Generates a hash code for the message format object.
- Overrides:
-
hashCode
in classObject
- Returns:
- a hash code value for this object.
- See Also:
-
Object.equals(java.lang.Object)
,System.identityHashCode(java.lang.Object)