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## java.text
Class MessageFormat

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

All Implemented Interfaces:
  Cloneable, Serializable

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);

>      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:

>      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
>      output: The disk "MyDisk" contains 0 file(s).
>      output: The disk "MyDisk" contains 1 file(s).
>      output: 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.

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,

     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 occurances of the same argument would return the last match. For 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")}

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`, Serialized Form

Constructor Summary
`MessageFormat(String pattern)` Constructs with the specified pattern.

Method Summary
`void` | `applyPattern(String newPattern)` Sets the pattern.
`Object` | `clone()` Overrides Cloneable
`boolean` | `equals(Object obj)` Equality comparision between two message format objects
`StringBuffer` | `format(Object[] source, StringBuffer result, FieldPosition ignore)` Returns pattern with formatted objects.
`StringBuffer` | `format(Object source, StringBuffer result, FieldPosition ignore)` Returns pattern with formatted objects.
`static String` | `format(String pattern, Object[] arguments)` Convenience routine.
`Format[]` | `getFormats()` Gets formats that were set with setFormats.
`Locale` | `getLocale()` Gets the locale.
`int` | `hashCode()` Generates a hash code for the message format object.
`Object[]` | `parse(String source)` Parses the string.
`Object[]` | `parse(String source, ParsePosition status)` Parses the string.
`Object` | `parseObject(String text, ParsePosition status)` Parses the string.
`void` | `setFormat(int variable, Format newFormat)` Set a format to be used on a variable in the pattern.
`void` | `setFormats(Format[] newFormats)` Sets formats to use on parameters.
`void` | `setLocale(Locale theLocale)` Constructs with the specified pattern and formats for the arguments in that pattern.
`String` | `toPattern()` Gets the pattern.

Methods inherited from class java.text.Format
`format, parseObject`

Methods inherited from class java.lang.Object
`finalize, getClass, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### MessageFormat

    public MessageFormat(String pattern)

  Constructs with the specified pattern.
  See Also:
    `applyPattern(java.lang.String)`

Method Detail

### setLocale

    public void setLocale(Locale theLocale)

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

### 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)

  Set a format to be used on a variable in the pattern.
  Parameters:
    `variable` - the zero-based number of the variable in the format. This is not the argument number. If `variable` is out of range, an `ArrayIndexOutOfBoundsException` is thrown.
    `newFormat` - the format to use for the specified variable

### 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. If source is null, the original pattern is returned, if source contains null objects, the formatted result will substitute each argument with the string "null".
  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)

  Returns pattern with formatted objects. If source is null, the original pattern is returned, if source contains null objects, the formatted result will substitute each argument with the string "null".
  Overrides:
    `format` in class `Format`
  Parameters:
    `source` - an array of objects to be formatted & substituted.
    `result` - where text is appended.
    `ignore` - no useful status is returned.

### 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 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 parsed more than once in the string, then the later parse wins.
  When the parse fails, use ParsePosition.getErrorIndex() to find out where in the string did the parsing failed. The returned error index is the starting offset of the sub-patterns that the string is comparing with. For example, if the parsing string "AAA {0} BBB" is comparing against the pattern "AAD {0} BBB", the error index is 0. When an error occurs, the call to this method will return null. If the soruce is null, return an empty array.

### 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`
  Following copied from class: `java.text.Format`
  Parameters:
    `status` - Input-Output parameter.

    Before calling, set status.index to the offset you want to start parsing at in the source. After calling, status.index is the end of the text you parsed. If error occurs, index is unchanged.

    When parsing, leading whitespace is discarded (with successful parse), while trailing whitespace is left as is.

    Example: Parsing "_12_xy" (where _ represents a space) for a number, with index == 0 will result in the number 12, with status.index updated to 3 (just before the second space). Parsing a second time will result in a ParseException since "xy" is not a number, and leave index at 3.

    Subclasses will typically supply specific parse methods that return different types of values. Since methods can't overload on return types, these will typically be named "parse", while this polymorphic method will always be called parseObject. Any parse method that does not take a status should throw ParseException when no text in the required format is at the start position.

  Returns:
    Object parsed from string. In case of error, returns null.
  See Also:
    `ParsePosition`

### clone

    public Object clone()

  Overrides Cloneable
  Overrides:
    `clone` in class `Format`
  Following copied from class: `java.lang.Object`
  Returns:
    a clone of this instance.
  Throws:
    `CloneNotSupportedException` - if the object's class does not support the `Cloneable` interface. Subclasses that override the `clone` method can also throw this exception to indicate that an instance cannot be cloned.
    `OutOfMemoryError` - if there is not enough memory.
  See Also:
    `Cloneable`

### equals

    public boolean equals(Object obj)

  Equality comparision between two message format objects
  Overrides:
    `equals` in class `Object`
  Following copied from class: `java.lang.Object`
  Parameters:
    `obj` - the reference object with which to compare.
  Returns:
    `true` if this object is the same as the obj argument; `false` otherwise.
  See Also:
    `Boolean.hashCode()`, `Hashtable`

### hashCode

    public int hashCode()

  Generates a hash code for the message format object.
  Overrides:
    `hashCode` in class `Object`
  Following copied from class: `java.lang.Object`
  Returns:
    a hash code value for this object.
  See Also:
    `Object.equals(java.lang.Object)`, `Hashtable`

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