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MessageFormat (Java SE 24 & JDK 24)
  1. java.base
  2. java.text
  3. MessageFormat
Contents 
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  1. Description
    1. Patterns and Their Interpretation
    1. Usage Information
    2. Formatting Date and Time
  2. Nested Class Summary
  3. Constructor Summary
  4. Method Summary
  5. Constructor Details
    1. MessageFormat(String)
    2. MessageFormat(String, Locale)
  6. Method Details
    1. setLocale(Locale)
    2. getLocale()
    3. applyPattern(String)
    4. toPattern()
    5. setFormatsByArgumentIndex(Format[])
    6. setFormats(Format[])
    7. setFormatByArgumentIndex(int, Format)
    8. setFormat(int, Format)
    9. getFormatsByArgumentIndex()
    10. getFormats()
    11. format(Object[], StringBuffer, FieldPosition)
    12. format(String, Object...)
    13. format(Object, StringBuffer, FieldPosition)
    14. formatToCharacterIterator(Object)
    15. parse(String, ParsePosition)
    16. parse(String)
    17. parseObject(String, ParsePosition)
    18. clone()
    19. equals(Object)
    20. hashCode()
    21. toString()

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 class 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:
         number
         dtf_date
         dtf_time
         dtf_datetime
         pre-defined DateTimeFormatter(s)
         date
         time
         choice
         list

 FormatStyle:
         short
         medium
         long
         full
         integer
         currency
         percent
         compact_short
         compact_long
         or
         unit
         SubformatPattern

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.

Any constructor or method that takes a String pattern parameter will throw an IllegalArgumentException if the pattern contains an ArgumentIndex value that is equal to or exceeds an implementation limit.

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. These values are case-insensitive when passed to applyPattern(String). Combinations not shown in the table are illegal. A SubformatPattern must be a valid pattern string for the Format subclass used.

Implementation Note:
In the reference implementation, the limit of ArgumentIndex is 10,000.
Shows how FormatType and FormatStyle values map to Format instances
FormatType FormatStyle Subformat Created
(none) (none) null
number (none) NumberFormat.getInstance(getLocale())
integer NumberFormat.getIntegerInstance(getLocale())
currency NumberFormat.getCurrencyInstance(getLocale())
percent NumberFormat.getPercentInstance(getLocale())
compact_short NumberFormat.getCompactNumberInstance(getLocale(), NumberFormat.Style.SHORT)
compact_long NumberFormat.getCompactNumberInstance(getLocale(), NumberFormat.Style.LONG)
SubformatPattern new DecimalFormat(subformatPattern, DecimalFormatSymbols.getInstance(getLocale()))
dtf_date (none) DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM).withLocale(getLocale())
short DateTimeFormatter.ofLocalizedDate(FormatStyle.SHORT).withLocale(getLocale())
medium DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM).withLocale(getLocale())
long DateTimeFormatter.ofLocalizedDate(FormatStyle.LONG).withLocale(getLocale())
full DateTimeFormatter.ofLocalizedDate(FormatStyle.FULL).withLocale(getLocale())
SubformatPattern DateTimeFormatter.ofPattern(subformatPattern, getLocale())
dtf_time (none) DateTimeFormatter.ofLocalizedTime(FormatStyle.MEDIUM).withLocale(getLocale())
short DateTimeFormatter.ofLocalizedTime(FormatStyle.SHORT).withLocale(getLocale())
medium DateTimeFormatter.ofLocalizedTime(FormatStyle.MEDIUM).withLocale(getLocale())
long DateTimeFormatter.ofLocalizedTime(FormatStyle.LONG).withLocale(getLocale())
full DateTimeFormatter.ofLocalizedTime(FormatStyle.FULL).withLocale(getLocale())
SubformatPattern DateTimeFormatter.ofPattern(subformatPattern, getLocale())
dtf_datetime (none) DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM).withLocale(getLocale())
short DateTimeFormatter.ofLocalizedDateTime(FormatStyle.SHORT).withLocale(getLocale())
medium DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM).withLocale(getLocale())
long DateTimeFormatter.ofLocalizedDateTime(FormatStyle.LONG).withLocale(getLocale())
full DateTimeFormatter.ofLocalizedDateTime(FormatStyle.FULL).withLocale(getLocale())
SubformatPattern DateTimeFormatter.ofPattern(subformatPattern, getLocale())
pre-defined DateTimeFormatter(s) (none) The pre-defined DateTimeFormatter(s) are used as a FormatType : BASIC_ISO_DATE, ISO_LOCAL_DATE, ISO_OFFSET_DATE, ISO_DATE, ISO_LOCAL_TIME, ISO_OFFSET_TIME, ISO_TIME, ISO_LOCAL_DATE_TIME, ISO_OFFSET_DATE_TIME, ISO_ZONED_DATE_TIME, ISO_DATE_TIME, ISO_ORDINAL_DATE, ISO_WEEK_DATE, ISO_INSTANT, RFC_1123_DATE_TIME
date (none) DateFormat.getDateInstance(DateFormat.DEFAULT, getLocale())
short DateFormat.getDateInstance(DateFormat.SHORT, getLocale())
medium DateFormat.getDateInstance(DateFormat.MEDIUM, 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.MEDIUM, getLocale())
long DateFormat.getTimeInstance(DateFormat.LONG, getLocale())
full DateFormat.getTimeInstance(DateFormat.FULL, getLocale())
SubformatPattern new SimpleDateFormat(subformatPattern, getLocale())
choice SubformatPattern new ChoiceFormat(subformatPattern)
list (none) ListFormat.getInstance(getLocale(), ListFormat.Type.STANDARD, ListFormat.Style.FULL)
or ListFormat.getInstance(getLocale(), ListFormat.Type.OR, ListFormat.Style.FULL)
unit ListFormat.getInstance(getLocale(), ListFormat.Type.UNIT, ListFormat.Style.FULL}

Quoting Rules in Patterns

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.

Usage Information

The following example demonstrates a general usage of MessageFormat. In internationalized programs, the message format pattern and other static strings will likely be obtained from resource bundles.
CopyCopy snippet [Copy snippet] 
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 GregorianCalendar(2053, Calendar.JULY, 3, 12, 30).getTime(), event);
result returns the following: 
 At 12:30:00 PM on Jul 3, 2053, there was a disturbance in the Force on planet 7.

For more sophisticated patterns, ChoiceFormat can be used with MessageFormat to produce accurate forms for singular and plural:

CopyCopy snippet [Copy snippet] 
MessageFormat msgFmt = new MessageFormat("The disk \"{0}\" contains {1,choice,0#no files|1#one file|1< {1,number,integer} files}.");
Object[] args = {"MyDisk", fileCount};
String result = msgFmt.format(args);
result with different values for fileCount, returns the following: 
 The disk "MyDisk" contains no files.
 The disk "MyDisk" contains one file.
 The disk "MyDisk" contains 1,273 files.

Notes: As seen in the previous snippet, the string produced by a ChoiceFormat in MessageFormat is treated as special; occurrences of '{' are used to indicate subformats, and cause recursion. If a FormatElement is defined in the ChoiceFormat pattern, it will only be formatted according to the FormatType and FormatStyle pattern provided. The associated subformats of the top level MessageFormat will not be applied to the FormatElement defined in the ChoiceFormat pattern. 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.

Formatting Date and Time

MessageFormat provides patterns that support the date/time formatters in the java.time.format and java.text packages. Consider the following three examples, with a date of 11/16/2023:

1) a date FormatType with a full FormatStyle,

CopyCopy snippet [Copy snippet] 
Object[] arg = {new GregorianCalendar(2023, Calendar.NOVEMBER, 16).getTime()};
var fmt = new MessageFormat("The date was {0,date,full}");
fmt.format(arg); // returns "The date was Thursday, November 16, 2023"

2) a dtf_date FormatType with a full FormatStyle,

CopyCopy snippet [Copy snippet] 
Object[] arg = {LocalDate.of(2023, 11, 16)};
var fmt = new MessageFormat("The date was {0,dtf_date,full}");
fmt.format(arg); // returns "The date was Thursday, November 16, 2023"

3) an ISO_LOCAL_DATE FormatType,

CopyCopy snippet [Copy snippet] 
Object[] arg = {LocalDate.of(2023, 11, 16)};
var fmt = new MessageFormat("The date was {0,ISO_LOCAL_DATE}");
fmt.format(arg); // returns "The date was 2023-11-16"

Parsing

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,

CopyCopy snippet [Copy snippet] 
MessageFormat mf = new MessageFormat("{0,number,#.##}, {0,number,#.#}");
Object[] objs = {Double.valueOf(3.1415)};
String result = mf.format( objs );
// result now equals "3.14, 3.1"
objs = mf.parse(result, new ParsePosition(0));
// objs now equals {Double.valueOf(3.1)}

Likewise, parsing with a MessageFormat object using patterns containing multiple occurrences of the same argument would return the last match. For example,

CopyCopy snippet [Copy snippet] 
MessageFormat mf = new MessageFormat("{0}, {0}, {0}");
String forParsing = "x, y, z";
Object[] objs = mf.parse(forParsing, new ParsePosition(0));
// objs 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:

Report a bug or suggest an enhancement
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