Class Format
- java.lang.Object
-
- java.text.Format
- All Implemented Interfaces:
-
Serializable
,Cloneable
- Direct Known Subclasses:
-
DateFormat
,MessageFormat
,NumberFormat
public abstract class Format extends Object implements Serializable, Cloneable
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.
- Since:
- 1.1
- See Also:
-
ParsePosition
,FieldPosition
,NumberFormat
,DateFormat
,MessageFormat
, Serialized Form
Nested Class Summary
Modifier and Type | Class | Description |
---|---|---|
static class | Format.Field | Defines constants that are used as attribute keys in the |
Constructor Summary
Modifier | Constructor | Description |
---|---|---|
protected | Format() | Sole constructor. |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
Object | clone() | Creates and returns a copy of this object. |
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. |
AttributedCharacterIterator | formatToCharacterIterator(Object obj) | Formats an Object producing an |
Object | 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 a string to produce an object. |
Methods declared in class java.lang.Object
equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Constructor Detail
Format
protected Format()
Sole constructor. (For invocation by subclass constructors, typically implicit.)
Method Detail
format
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
format
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
- 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 null -
IllegalArgumentException
- if the Format cannot format the given object
formatToCharacterIterator
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. - Since:
- 1.4
parseObject
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
- AString
, part of which should be parsed. -
pos
- AParsePosition
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
- ifsource
orpos
is null.
parseObject
public Object parseObject(String source) throws ParseException
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
- AString
whose beginning should be parsed. - Returns:
- An
Object
parsed from the string. - Throws:
-
ParseException
- if the beginning of the specified string cannot be parsed. -
NullPointerException
- ifsource
is null.
clone
public Object clone()
Creates and returns a copy of this object.