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# Class java.text.Format

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

public abstract class Format
extends Object
implements Serializable, Cloneable

`Format` is an abstract base class for formatting locale-sensitive information such as dates, messages, and numbers.

`Format` defines the programming interface for formatting locale-sensitive objects into `String`s (the `format` method) and for parsing `String`s back into objects (the `parseObject` method). Any `String` formatted by `format` is guaranteed to be parseable by `parseObject`.

If formatting is unsuccessful because the `Format` object cannot format the type of object specified, `format` throws an `IllegalArgumentException`. Otherwise, if there is something illformed about the object, `format` returns the Unicode replacement character `\\uFFFD`.

If there is no match when parsing, `parseObject(String)` throws a `ParseException`, and `parseObject(String, ParsePosition)` leaves the `ParsePosition` `index` member unchanged and returns `null`.

Subclassing: The JDK provides three concrete subclasses of `Format`-- `DateFormat`, `MessageFormat`, and `NumberFormat`--for formatting dates, messages, and numbers, respectively.

Concrete subclasses must implement these two methods:

1. `format(Object obj, StringBuffer toAppendTo, FieldPosition pos)`
2. `parseObject (String source, ParsePosition pos)`

Most subclasses will also implement the following two methods:

1. `getInstance` for getting a useful format object appropriate for the current locale
2. `getInstance(Locale)` for getting a useful format object appropriate for the specified locale

In addition, some subclasses may also choose to implement other `getXxxxInstance` methods for more specialized control. For example, the `NumberFormat` class provides `getPercentInstance` and `getCurrencyInstance` methods for getting specialized number formatters.

Subclasses of `Format` that allow programmers to create objects for locales (with `getInstance(Locale)` for example) must also implement the following class method:

>      public static Locale[] getAvailableLocales()

And finally subclasses may define a set of constants to identify the various fields in the formatted output. These constants are used to create a FieldPosition object which identifies what information is contained in the field and its position in the formatted result. These constants should be named `item_FIELD` where `item` identifies the field. For examples of these constants, see `ERA_FIELD` and its friends in `DateFormat`.

See Also:
  ParsePosition, FieldPosition, NumberFormat, DateFormat, MessageFormat

##

Format()

##

clone()
  Creates a new object of the same class as this object.
format(Object)
  Formats an object to produce a string.
format(Object, StringBuffer, FieldPosition)
  Formats an object to produce a string.
parseObject(String)
  Parses a string to produce an object.
parseObject(String, ParsePosition)
  Parses a string to produce an object.

##

Format

     public Format()

##

format

     public final String format(Object obj)

  Formats an object to produce a string.

  Subclasses will override the StringBuffer version of format.

  Parameters:
    obj - The object to format
  Returns:
    Formatted string.
  Throws: IllegalArgumentException
    when the Format cannot format the type of object.
  See Also:
    MessageFormat, format

format

     public abstract StringBuffer format(Object obj,
                                         StringBuffer toAppendTo,
                                         FieldPosition pos)

  Formats an object to produce a string. Subclasses will implement for particular object, such as:

       StringBuffer format (Number obj, StringBuffer toAppendTo)
       Number parse (String str)

  These general routines allow polymorphic parsing and formatting for objects such as the MessageFormat.

  Parameters:
    obj - The object to format
    toAppendTo - where the text is to be appended
    status - On input: an alignment field, if desired. On output: the offsets of the alignment field.
  Returns:
    the value passed in as toAppendTo (this allows chaining, as with StringBuffer.append())
  Throws: IllegalArgumentException
    when the Format cannot format the given object.
  See Also:
    MessageFormat, FieldPosition

parseObject

     public abstract Object parseObject(String source,
                                        ParsePosition status)

  Parses a string to produce an object. Subclasses will typically implement for particular object, such as:

             String format (Number obj);
             String format (long obj);
             String format (double obj);
             Number parse (String str);

  Parameters:
    ParsePosition - 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

parseObject

     public Object parseObject(String source) throws ParseException

  Parses a string to produce an object.

  Throws: ParseException
    if the specified string is invalid.

clone

     public Object clone()

  Creates a new object of the same class as this object.

  Overrides:
    clone in class Object

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