Produces concatenated messages in language-neutral way. New code should probably use Java.Util.Formatter instead.

MessageFormat takes a set of objects, formats them and 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:

java Example

MessageFormatPattern:StringMessageFormatPatternFormatElementStringFormatElement:
         { ArgumentIndex }
         { ArgumentIndex , FormatType }
         { ArgumentIndex , FormatType , FormatStyle }
 FormatType: one of 
         number date time choice
 FormatStyle:
         short
         medium
         long
         full
         integer
         currency
         percent
         SubformatPatternString:StringPart<sub>opt</sub>StringStringPartStringPart:
         ''
         ' QuotedString '
         UnquotedStringSubformatPattern:SubformatPatternPart<sub>opt</sub>SubformatPatternSubformatPatternPartSubFormatPatternPart:
         ' 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,$'#',##"} will produce a number format with the hash-sign quoted, with a result such as: "$#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.

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.

Note also that the simplest way to avoid the problem is to use the real apostrophe (single quote) character ’ (') for human-readable text, and to use the ASCII apostrophe (' ' ) only in program syntax, like quoting in MessageFormat. See the annotations for U+0027 Apostrophe in The Unicode Standard.

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)		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)

Usage Information

Here are some examples of usage:

java Example

 Object[] arguments = {
         Integer.valueOf(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:

java Example

 Object[] testArgs = {Long.valueOf(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).
 

For more sophisticated patterns, you can use a ChoiceFormat to get output such as:

java Example

 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 = {Long.valueOf(12373), "MyDisk"};
 System.out.println(form.format(testArgs));
 
 Output (with different testArgs):
 
 The disk "MyDisk" contains no files.
 The disk "MyDisk" contains one file.
 The disk "MyDisk" contains 1,273 files.
 

You can either do this programmatically, as in the above example, or by using a pattern (see Java.Text.ChoiceFormat for more information) as in:

java Example

 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:

java 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:

java 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.

See Also

• Java.Util.Formatter

[Android Documentation]

Namespace: Java.Text
Assembly: Mono.Android (in Mono.Android.dll)
Assembly Versions: 0.0.0.0
Since: Added in API level 1