public abstract class Format extends Object
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.
The Java 2 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.
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.
ParsePosition
,
FieldPosition
,
NumberFormat
Modifier and Type | Class and Description |
---|---|
static class |
Format.Field
Defines constants that are used as attribute keys in the
AttributedCharacterIterator returned from
Format.formatToCharacterIterator and as field identifiers in FieldPosition . |
Constructor and Description |
---|
Format() |
Modifier and Type | Method and Description |
---|---|
String |
format(Object obj)
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.
|
public Format()
public final String format(Object obj)
format
(obj, new StringBuffer(), new FieldPosition(0)).toString();
obj
- The object to formatIllegalArgumentException
- if the Format cannot format the given objectpublic abstract StringBuffer format(Object obj, StringBuffer toAppendTo, FieldPosition pos)
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.obj
- The object to formattoAppendTo
- where the text is to be appendedpos
- A FieldPosition
identifying a field in the formatted texttoAppendTo
, with formatted text appendedNullPointerException
- if toAppendTo
or pos
is nullIllegalArgumentException
- if the Format cannot format the given objectCopyright © 2005–2017 Jean-Marie Dautelle, Werner Keil, V2COM. All rights reserved.