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 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.
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:
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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:
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getInstancefor 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:
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Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionstatic classDefines constants that are used as attribute keys in theAttributedCharacterIteratorreturned fromFormat.formatToCharacterIteratorand as field identifiers inFieldPosition. -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionclone()Creates and returns a copy of this object.final StringFormats an object to produce a string.abstract StringBufferformat(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 ObjectparseObject(String source, ParsePosition pos) Parses text from the given string to produce an object.
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Constructor Details
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Format
protected Format()Sole constructor. (For invocation by subclass constructors, typically implicit.)
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Method Details
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format
Formats an object to produce a string.- Implementation Requirements:
- This method returns a string that would be equal to the string returned by
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
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format
Formats an object and appends the resulting text to a given string buffer. If theposargument 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- AFieldPositionidentifying a field in the formatted text- Returns:
- the string buffer passed in as
toAppendTo, with formatted text appended - Throws:
NullPointerException- iftoAppendToorposis nullIllegalArgumentException- if the Format cannot format the given object
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formatToCharacterIterator
Formats an Object producing anAttributedCharacterIterator. You can use the returnedAttributedCharacterIteratorto 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 eachFormatimplementation to define what the legal values are for each attribute in theAttributedCharacterIterator, but typically the attribute key is also used as the attribute value.- API Note:
- Subclasses that support fields should override this and create an
AttributedCharacterIteratorwith meaningful attributes. - Implementation Requirements:
- The default implementation creates an
AttributedCharacterIteratorwith no 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
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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 ofposis 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 updatedposcan be used to indicate the starting point for the next call to this method. If an error occurs, then the index ofposis not changed, the error index ofposis set to the index of the character where the error occurred, andnullis returned.- Parameters:
source- theStringto parsepos- AParsePositionobject with index and error index information as described above.- Returns:
- An
Objectparsed from the string. In case of error, returnsnull. - Throws:
NullPointerException- ifsourceorposisnull.
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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
Objectparsed from the string. - Throws:
ParseException- if parsing failsNullPointerException- ifsourceisnull.
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clone
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