Class Format
- All Implemented Interfaces:
Serializable
,Cloneable
- Direct Known Subclasses:
DateFormat
,ListFormat
,MessageFormat
,NumberFormat
Format
is an abstract base class for formatting locale-sensitive
information such as dates, messages, numbers, and lists.
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).
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.
Subclassing
The Java Platform provides specialized subclasses of Format
--
DateFormat
, MessageFormat
, NumberFormat
, and
ListFormat
--for formatting dates, messages, numbers, and lists
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()
Subclasses may also consider implementing leniency when parsing. The definition of leniency should be delegated to the subclass.
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
.
Synchronization
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.
- Since:
- 1.1
- See Also:
-
Nested Class Summary
Modifier and TypeClassDescriptionstatic class
Defines constants that are used as attribute keys in theAttributedCharacterIterator
returned fromFormat.formatToCharacterIterator
and as field identifiers inFieldPosition
. -
Constructor Summary
-
Method Summary
Modifier and TypeMethodDescriptionclone()
Creates and returns a copy of this object.final String
Formats an object to produce a string.abstract StringBuffer
format
(Object obj, StringBuffer toAppendTo, FieldPosition pos) Formats an object and appends the resulting text to a given string buffer.Formats an Object producing anAttributedCharacterIterator
.parseObject
(String source) Parses text from the beginning of the given string to produce an object.abstract Object
parseObject
(String source, ParsePosition pos) Parses text from the given string to produce an object.
-
Constructor Details
-
Format
protected Format()Sole constructor. (For invocation by subclass constructors, typically implicit.)
-
-
Method Details
-
format
Formats an object to produce a string. This is equivalent toformat
(obj, new StringBuffer(), new FieldPosition(0)).toString();
- Parameters:
obj
- The object to format- Returns:
- Formatted string.
- Throws:
IllegalArgumentException
- if the Format cannot format the given object
-
format
Formats an object and appends the resulting text to a given string buffer. If thepos
argument identifies a field used by the format, then its indices are set to the beginning and end of the first such field encountered.- Parameters:
obj
- The object to formattoAppendTo
- where the text is to be appendedpos
- AFieldPosition
identifying a field in the formatted text- Returns:
- the string buffer passed in as
toAppendTo
, with formatted text appended - Throws:
NullPointerException
- iftoAppendTo
orpos
is nullIllegalArgumentException
- if the Format cannot format the given object
-
formatToCharacterIterator
Formats an Object producing anAttributedCharacterIterator
. You can use the returnedAttributedCharacterIterator
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 eachFormat
implementation to define what the legal values are for each attribute in theAttributedCharacterIterator
, 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 anAttributedCharacterIterator
with meaningful attributes.- Parameters:
obj
- The object to format- Returns:
- AttributedCharacterIterator describing the formatted value.
- Throws:
NullPointerException
- if obj is null.IllegalArgumentException
- when the Format cannot format the given object.- Since:
- 1.4
-
parseObject
Parses text from the given string to produce an object.This method attempts to parse text starting at the index given by
pos
. If parsing succeeds, then the index ofpos
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 updatedpos
can be used to indicate the starting point for the next call to this method. If an error occurs, then the index ofpos
is not changed, the error index ofpos
is set to the index of the character where the error occurred, andnull
is returned.- Parameters:
source
- theString
to parsepos
- AParsePosition
object with index and error index information as described above.- Returns:
- An
Object
parsed from the string. In case of error, returnsnull
. - Throws:
NullPointerException
- ifsource
orpos
isnull
.
-
parseObject
Parses text from the beginning of the given string to produce an object. This method may not use the entire text of the given string.- Parameters:
source
- AString
, to be parsed from the beginning.- Returns:
- An
Object
parsed from the string. - Throws:
ParseException
- if parsing failsNullPointerException
- ifsource
isnull
.
-
clone
-