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 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.
*
*
* 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 {@link DateFormat}.
*
*
* 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. * * @see java.text.ParsePosition * @see java.text.FieldPosition * @see java.text.NumberFormat * @see java.text.DateFormat * @see java.text.MessageFormat * @author Mark Davis */ public abstract class Format implements Serializable, Cloneable { private static final long serialVersionUID = -299282585814624189L; /** * Sole constructor. (For invocation by subclass constructors, typically * implicit.) */ protected Format() { } /** * Formats an object to produce a string. This is equivalent to *
* {@link #format(Object, StringBuffer, FieldPosition) format}(obj,
* new StringBuffer(), new FieldPosition(0)).toString();
*
*
* @param obj The object to format
* @return Formatted string.
* @exception IllegalArgumentException if the Format cannot format the given
* object
*/
public final String format (Object obj) {
return format(obj, new StringBuffer(), new FieldPosition(0)).toString();
}
/**
* 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.
*
* @param obj The object to format
* @param toAppendTo where the text is to be appended
* @param pos A FieldPosition identifying a field
* in the formatted text
* @return the string buffer passed in as toAppendTo,
* with formatted text appended
* @exception NullPointerException if toAppendTo or
* pos is null
* @exception IllegalArgumentException if the Format cannot format the given
* object
*/
public abstract StringBuffer format(Object obj,
StringBuffer toAppendTo,
FieldPosition pos);
/**
* 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.
*
* @exception NullPointerException if obj is null.
* @exception IllegalArgumentException when the Format cannot format the
* given object.
* @param obj The object to format
* @return AttributedCharacterIterator describing the formatted value.
* @since 1.4
*/
public AttributedCharacterIterator formatToCharacterIterator(Object obj) {
return createAttributedCharacterIterator(format(obj));
}
/**
* 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.
*
* @param source A String, part of which should be parsed.
* @param pos A ParsePosition object with index and error
* index information as described above.
* @return An Object parsed from the string. In case of
* error, returns null.
* @exception NullPointerException if pos is null.
*/
public abstract Object parseObject (String source, ParsePosition pos);
/**
* 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.
*
* @param source A String whose beginning should be parsed.
* @return An Object parsed from the string.
* @exception ParseException if the beginning of the specified string
* cannot be parsed.
*/
public Object parseObject(String source) throws ParseException {
ParsePosition pos = new ParsePosition(0);
Object result = parseObject(source, pos);
if (pos.index == 0) {
throw new ParseException("Format.parseObject(String) failed",
pos.errorIndex);
}
return result;
}
/**
* Creates and returns a copy of this object.
*
* @return a clone of this instance.
*/
public Object clone() {
try {
return super.clone();
} catch (CloneNotSupportedException e) {
// will never happen
throw new InternalError(e);
}
}
//
// Convenience methods for creating AttributedCharacterIterators from
// different parameters.
//
/**
* Creates an AttributedCharacterIterator for the String
* s.
*
* @param s String to create AttributedCharacterIterator from
* @return AttributedCharacterIterator wrapping s
*/
AttributedCharacterIterator createAttributedCharacterIterator(String s) {
AttributedString as = new AttributedString(s);
return as.getIterator();
}
/**
* Creates an AttributedCharacterIterator containg the
* concatenated contents of the passed in
* AttributedCharacterIterators.
*
* @param iterators AttributedCharacterIterators used to create resulting
* AttributedCharacterIterators
* @return AttributedCharacterIterator wrapping passed in
* AttributedCharacterIterators
*/
AttributedCharacterIterator createAttributedCharacterIterator(
AttributedCharacterIterator[] iterators) {
AttributedString as = new AttributedString(iterators);
return as.getIterator();
}
/**
* Returns an AttributedCharacterIterator with the String
* string and additional key/value pair key,
* value.
*
* @param string String to create AttributedCharacterIterator from
* @param key Key for AttributedCharacterIterator
* @param value Value associated with key in AttributedCharacterIterator
* @return AttributedCharacterIterator wrapping args
*/
AttributedCharacterIterator createAttributedCharacterIterator(
String string, AttributedCharacterIterator.Attribute key,
Object value) {
AttributedString as = new AttributedString(string);
as.addAttribute(key, value);
return as.getIterator();
}
/**
* Creates an AttributedCharacterIterator with the contents of
* iterator and the additional attribute key
* value.
*
* @param iterator Initial AttributedCharacterIterator to add arg to
* @param key Key for AttributedCharacterIterator
* @param value Value associated with key in AttributedCharacterIterator
* @return AttributedCharacterIterator wrapping args
*/
AttributedCharacterIterator createAttributedCharacterIterator(
AttributedCharacterIterator iterator,
AttributedCharacterIterator.Attribute key, Object value) {
AttributedString as = new AttributedString(iterator);
as.addAttribute(key, value);
return as.getIterator();
}
/**
* Defines constants that are used as attribute keys in the
* AttributedCharacterIterator returned
* from Format.formatToCharacterIterator and as
* field identifiers in FieldPosition.
*
* @since 1.4
*/
public static class Field extends AttributedCharacterIterator.Attribute {
// Proclaim serial compatibility with 1.4 FCS
private static final long serialVersionUID = 276966692217360283L;
/**
* Creates a Field with the specified name.
*
* @param name Name of the attribute
*/
protected Field(String name) {
super(name);
}
}
/**
* FieldDelegate is notified by the various Format
* implementations as they are formatting the Objects. This allows for
* storage of the individual sections of the formatted String for
* later use, such as in a FieldPosition or for an
* AttributedCharacterIterator.
*
* Delegates should NOT assume that the Format will notify
* the delegate of fields in any particular order.
*
* @see FieldPosition#getFieldDelegate
* @see CharacterIteratorFieldDelegate
*/
interface FieldDelegate {
/**
* Notified when a particular region of the String is formatted. This
* method will be invoked if there is no corresponding integer field id
* matching attr.
*
* @param attr Identifies the field matched
* @param value Value associated with the field
* @param start Beginning location of the field, will be >= 0
* @param end End of the field, will be >= start and <= buffer.length()
* @param buffer Contains current formatted value, receiver should
* NOT modify it.
*/
public void formatted(Format.Field attr, Object value, int start,
int end, StringBuffer buffer);
/**
* Notified when a particular region of the String is formatted.
*
* @param fieldID Identifies the field by integer
* @param attr Identifies the field matched
* @param value Value associated with the field
* @param start Beginning location of the field, will be >= 0
* @param end End of the field, will be >= start and <= buffer.length()
* @param buffer Contains current formatted value, receiver should
* NOT modify it.
*/
public void formatted(int fieldID, Format.Field attr, Object value,
int start, int end, StringBuffer buffer);
}
}