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 Strings (the
format method) and for parsing Strings back
into objects (the parseObject method).
Generally, a format's parseObject method must be able to parse
any string formatted by its format method. However, there may
be exceptional cases where this is not possible. For example, a
format method might create two adjacent integer numbers with
no separator in between, and in this case the parseObject could
not tell which digits belong to which number.
The Java Platform provides three specialized subclasses of Format--
DateFormat, MessageFormat, and
NumberFormat--for formatting dates, messages, and numbers,
respectively.
Concrete subclasses must implement three methods:
format(Object obj, StringBuffer toAppendTo, FieldPosition pos)
formatToCharacterIterator(Object obj)
parseObject(String source, ParsePosition pos)
MessageFormat.
Subclasses often also provide additional format methods for
specific input types as well as parse methods for specific
result types. Any parse method that does not take a
ParsePosition argument should throw ParseException
when no text in the required format is at the beginning of the input text.
Most subclasses will also implement the following factory methods:
getInstance for getting a useful format object appropriate
for the current locale
getInstance(Locale) for getting a useful format
object appropriate for the specified locale
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
Formats are generally 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.
ParsePositionFieldPositionNumberFormatDateFormatMessageFormatformat(obj, new StringBuffer(), new FieldPosition(0)).toString();
obj The object to formatjava.lang.IllegalArgumentException if the Format cannot format the given
objectpos argument identifies a field used by the format,
then its indices are set to the beginning and end of the first such
field encountered.
obj The object to formattoAppendTo where the text is to be appendedpos A FieldPosition identifying a field
in the formatted texttoAppendTo,
with formatted text appendedjava.lang.NullPointerException if toAppendTo or
pos is nulljava.lang.IllegalArgumentException if the Format cannot format the given
objectAttributedCharacterIterator.
You can use the returned AttributedCharacterIterator
to build the resulting String, as well as to determine information
about the resulting String.
Each attribute key of the AttributedCharacterIterator will be of type
Field. It is up to each Format implementation
to define what the legal values are for each attribute in the
AttributedCharacterIterator, but typically the attribute
key is also used as the attribute value.
The default implementation creates an
AttributedCharacterIterator with no attributes. Subclasses
that support fields should override this and create an
AttributedCharacterIterator with meaningful attributes.
obj The object to formatjava.lang.NullPointerException if obj is null.java.lang.IllegalArgumentException when the Format cannot format the
given object.
The method attempts to parse text starting at the index given by
pos.
If parsing succeeds, then the index of pos is updated
to the index after the last character used (parsing does not necessarily
use all characters up to the end of the string), and the parsed
object is returned. The updated pos can be used to
indicate the starting point for the next call to this method.
If an error occurs, then the index of pos is not
changed, the error index of pos is set to the index of
the character where the error occurred, and null is returned.
source A String, part of which should be parsed.pos A ParsePosition object with index and error
index information as described above.Object parsed from the string. In case of
error, returns null.java.lang.NullPointerException if pos is null.source A String whose beginning should be parsed.Object parsed from the string.ParseException if the beginning of the specified string
cannot be parsed.AttributedCharacterIterator containg the
concatenated contents of the passed in
AttributedCharacterIterators.
iterators AttributedCharacterIterators used to create resulting
AttributedCharacterIteratorsstring and additional key/value pair key,
value.
string String to create AttributedCharacterIterator fromkey Key for AttributedCharacterIteratorvalue Value associated with key in AttributedCharacterIteratoriterator and the additional attribute key
value.
iterator Initial AttributedCharacterIterator to add arg tokey Key for AttributedCharacterIteratorvalue Value associated with key in AttributedCharacterIteratorFormat
implementations as they are formatting the Objects. This allows for
storage of the individual sections of the formatted String for
later use, such as in a FieldPosition or for an
AttributedCharacterIterator.
Delegates should NOT assume that the Format will notify
the delegate of fields in any particular order.
FieldPosition.DelegateCharacterIteratorFieldDelegateattr.
attr Identifies the field matchedvalue Value associated with the fieldstart Beginning location of the field, will be >= 0end End of the field, will be >= start and <= buffer.length()buffer Contains current formatted value, receiver should
NOT modify it.fieldID Identifies the field by integerattr Identifies the field matchedvalue Value associated with the fieldstart Beginning location of the field, will be >= 0end End of the field, will be >= start and <= buffer.length()buffer Contains current formatted value, receiver should
NOT modify it.