Class java.text.MessageFormat





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Class java.text.MessageFormat


java.lang.Object
|
+----java.text.Format
|
+----java.text.MessageFormat



public class MessageFormat
extends Format

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
doesn't require any complex setup for a given locale. In fact,
MessageFormat doesn't implement any locale specific behavior
at all. It just needs to be set up on a sentence by sentence basis.

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);
: 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
: The disk "MyDisk" contains 0 file(s).
: The disk "MyDisk" contains 1 file(s).
: The disk "MyDisk" contains 1,273 file(s).



The pattern is of the form:


messageFormatPattern := string ( "{" messageFormatElement "}" string )*
messageFormatElement := argument { "," elementFormat }
elementFormat := "time" { "," datetimeStyle }
| "date" { "," datetimeStyle }
| "number" { "," numberStyle }
| "choice" { "," choiceStyle }
datetimeStyle := "short"
| "medium"
| "long"
| "full"
| dateFormatPattern
numberStyle := "currency"
| "percent"
| "integer"
| numberFormatPattern
choiceStyle := choiceFormatPattern


If there is no elementFormat,
then the argument must be a string, which is substituted. If there is
no dateTimeStyle or numberStyle, then the
default format is used (for example, NumberFormat.getInstance,
DateFormat.getTimeInstance, or DateFormat.getInstance).

In strings, single quotes can be used to quote the "{"
(curly brace) if necessary. A real single quote is represented by ''.
Inside a messageFormatElement, quotes are not
removed. For example, {1,number,$'#',##} will produce a number format
with the pound-sign quoted, with a result such as: "$#31,45".

If a pattern is used, then unquoted braces in the pattern, if any, must match:
that is, "ab {0} de" and "ab '}' de" are ok, but "ab {0'}' de" and "ab } de" are
not.

The argument is a number from 0 to 9, which corresponds to the
arguments presented in an array to be formatted.

It is ok to have unused arguments in the array.
With missing arguments or arguments that are not of the right class for
the specified format, a ParseException is thrown.
First, format checks to see if a Format object has been
specified for the argument with the setFormats method.
If so, then format uses that Format object to format the
argument. Otherwise, the argument is formatted based on the object's
type. If the argument is a Number, then format
uses NumberFormat.getInstance to format the argument; if the
argument is a Date, then format uses
DateFormat.getDateTimeInstance to format the argument.
Otherwise, it uses the toString method.

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.setFormat(1,fileform); // NOT zero, see below
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.

Note: formats are numbered by order of
variable in the string.
This is not the same as the argument numbering!
For example: with "abc{2}def{3}ghi{0}...",

format0 affects the first variable {2}
format1 affects the second variable {3}
format2 affects the second variable {0}
and so on.


You can use setLocale followed by applyPattern
(and then possibly setFormat) to re-initialize a
MessageFormat with a different locale.


See Also:
Locale, Format, NumberFormat, DecimalFormat, ChoiceFormat








MessageFormat(String)
Constructs with the specified pattern.






applyPattern(String)
Sets the pattern.

clone()
Overrides Cloneable


equals(Object)
Equality comparision between two message format objects


format(Object, StringBuffer, FieldPosition)
Formats an object to produce a string.

format(Object[], StringBuffer, FieldPosition)
Returns pattern with formatted objects.

format(String, Object[])
Convenience routine.

getFormats()
Gets formats that were set with setFormats.

getLocale()
Gets the locale.

hashCode()
Generates a hash code for the message format object.

parse(String)
Parses the string.

parse(String, ParsePosition)
Parses the string.

parseObject(String, ParsePosition)
Parses the string.

setFormat(int, Format)
Sets formats individually to use on parameters.

setFormats(Format[])
Sets formats to use on parameters.

setLocale(Locale)
Constructs with the specified pattern and formats for the
arguments in that pattern.

toPattern()
Gets the pattern.







MessageFormat

public MessageFormat(String pattern)


Constructs with the specified pattern.


See Also:
applyPattern







setLocale

public void setLocale(Locale theLocale)


Constructs with the specified pattern and formats for the
arguments in that pattern.


See Also:
setPattern



getLocale

public Locale getLocale()


Gets the locale. This locale is used for fetching default number or date
format information.



applyPattern

public void applyPattern(String newPattern)


Sets the pattern. See the class description.



toPattern

public String toPattern()


Gets the pattern. See the class description.



setFormats

public void setFormats(Format newFormats[])


Sets formats to use on parameters.
See the class description about format numbering.



setFormat

public void setFormat(int variable,
Format newFormat)


Sets formats individually to use on parameters.
See the class description about format numbering.



getFormats

public Format[] getFormats()


Gets formats that were set with setFormats.
See the class description about format numbering.



format

public final StringBuffer format(Object source[],
StringBuffer result,
FieldPosition ignore)


Returns pattern with formatted objects.


Parameters:
source - an array of objects to be formatted & substituted.
result - where text is appended.
ignore - no useful status is returned.



format

public static String format(String pattern,
Object arguments[])


Convenience routine.
Avoids explicit creation of MessageFormat,
but doesn't allow future optimizations.



format

public final StringBuffer format(Object source,
StringBuffer result,
FieldPosition ignore)


Formats an object to produce a string.


Overrides:
format in class Format



parse

public Object[] parse(String source,
ParsePosition status)


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 is 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 formatted twice in the string,
then the later parse wins.




parse

public Object[] parse(String source) throws ParseException


Parses the string. Does not yet handle recursion (where
the substituted strings contain {n} references.)


Throws: ParseException
if the string can't be parsed.



parseObject

public Object parseObject(String text,
ParsePosition status)


Parses the string. Does not yet handle recursion (where
the substituted strings contain %n references.)


Overrides:
parseObject in class Format



clone

public Object clone()


Overrides Cloneable


Overrides:
clone in class Format



equals

public boolean equals(Object obj)


Equality comparision between two message format objects


Overrides:
equals in class Object



hashCode

public int hashCode()


Generates a hash code for the message format object.


Overrides:
hashCode in class Object




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