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);
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 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}...",