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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
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:
Typically, the message format will come from resources, and the arguments will be dynamically set at runtime.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);
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:
If there is nomessageFormatPattern := 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
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:
You can either do this programmatically, as in the above example, or by using a pattern (seeMessageFormat 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.
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}...",
You can use setLocale
followed by applyPattern
(and then possibly setFormat
) to re-initialize a
MessageFormat
with a different locale.
public MessageFormat(String pattern)
public void setLocale(Locale theLocale)
public Locale getLocale()
public void applyPattern(String newPattern)
public String toPattern()
public void setFormats(Format newFormats[])
public void setFormat(int variable, Format newFormat)
public Format[] getFormats()
public final StringBuffer format(Object source[], StringBuffer result, FieldPosition ignore)
public static String format(String pattern, Object arguments[])
public final StringBuffer format(Object source, StringBuffer result, FieldPosition ignore)
public Object[] parse(String source, ParsePosition status)
Caveats: The parse may fail in a number of circumstances. For example:
public Object[] parse(String source) throws ParseException
public Object parseObject(String text, ParsePosition status)
public Object clone()
public boolean equals(Object obj)
public int hashCode()
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