Known Direct Subclasses |
Known Indirect Subclasses |
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).
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 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
.
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.
Nested Class Summary
class | Format.Field | Defines constants that are used as attribute keys in the
AttributedCharacterIterator returned
from Format.formatToCharacterIterator and as
field identifiers in FieldPosition . |
Protected Constructor Summary
Format()
Sole constructor.
|
Public Method Summary
Object |
clone()
Creates and returns a copy of this object.
|
final String | |
abstract StringBuffer |
format(Object obj, StringBuffer toAppendTo, FieldPosition pos)
Formats an object and appends the resulting text to a given string
buffer.
|
AttributedCharacterIterator | |
Object | |
abstract Object |
Inherited Method Summary
Protected Constructors
protected Format ()
Sole constructor. (For invocation by subclass constructors, typically implicit.)
Public Methods
public final String format (Object obj)
Formats an object to produce a string. This is equivalent to
format
(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 |
---|
public abstract StringBuffer format (Object obj, StringBuffer toAppendTo, FieldPosition pos)
Formats an object and appends the resulting text to a given string
buffer.
If the pos
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 format |
---|---|
toAppendTo | where the text is to be appended |
pos | A FieldPosition identifying a field
in the formatted text |
Returns
- the string buffer passed in as
toAppendTo
, with formatted text appended
Throws
NullPointerException | if toAppendTo or
pos is null |
---|---|
IllegalArgumentException | if the Format cannot format the given object |
public AttributedCharacterIterator formatToCharacterIterator (Object obj)
Formats an Object producing an AttributedCharacterIterator
.
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.
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. |
public Object parseObject (String source)
Parses text from the beginning of the given string to produce an object. The method may not use the entire text of the given string.
Parameters
source | A String whose beginning should be parsed. |
---|
Returns
- An
Object
parsed from the string.
Throws
ParseException | if the beginning of the specified string cannot be parsed. |
---|
public abstract Object parseObject (String source, ParsePosition pos)
Parses text from a string to produce an 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.
Parameters
source | A String , part of which should be parsed. |
---|---|
pos | A ParsePosition object with index and error
index information as described above. |
Returns
- An
Object
parsed from the string. In case of error, returns null.
Throws
NullPointerException | if pos is null.
|
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