Class Format

java.lang.Object
java.text.Format
All Implemented Interfaces:
Serializable,Cloneable
Direct Known Subclasses:
DateFormat,ListFormat,MessageFormat,NumberFormat
public abstract classFormatextendsObjectimplementsSerializable,Cloneable
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 intoStrings (theformat method) and for parsingStrings back into objects (theparseObject method).

Generally, a format'sparseObject method must be able to parse any string formatted by itsformat method. However, there may be exceptional cases where this is not possible. For example, aformat method might create two adjacent integer numbers with no separator in between, and in this case theparseObject could not tell which digits belong to which number.

Subclassing

The Java Platform provides specialized subclasses ofFormat--DateFormat,MessageFormat,NumberFormat, andListFormat--for formatting dates, messages, numbers, and lists respectively.

Concrete subclasses must implement three methods:

  1. format(Object obj, StringBuffer toAppendTo, FieldPosition pos)
  2. formatToCharacterIterator(Object obj)
  3. parseObject(String source, ParsePosition pos)
These general methods allow polymorphic parsing and formatting of objects and are used, for example, byMessageFormat. Subclasses often also provide additionalformat methods for specific input types as well asparse methods for specific result types. Anyparse method that does not take aParsePosition argument should throwParseException when no text in the required format is at the beginning of the input text.

Most subclasses will also implement the following factory methods:

  1. getInstance for getting a useful format object appropriate for the current locale
  2. getInstance(Locale) for getting a useful format object appropriate for the specified locale
In addition, some subclasses may also implement othergetXxxxInstance methods for more specialized control. For example, theNumberFormat class providesgetPercentInstance andgetCurrencyInstance methods for getting specialized number formatters.

Subclasses ofFormat that allow programmers to create objects for locales (withgetInstance(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 nameditem_FIELD whereitem identifies the field. For examples of these constants, seeERA_FIELD and its friends inDateFormat.

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:

  • Constructor Details

    • Format

      protected Format()
      Sole constructor. (For invocation by subclass constructors, typically implicit.)

  • Method Details

    • format

      public final String format(Object obj)
      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

    • 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 thepos 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 astoAppendTo, 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 anAttributedCharacterIterator. You can use the returnedAttributedCharacterIterator to build the resulting String, as well as to determine information about the resulting String.

      Each attribute key of the AttributedCharacterIterator will be of typeField. It is up to eachFormat implementation 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 anAttributedCharacterIterator with meaningful attributes.
      Implementation Requirements:
      The default implementation creates anAttributedCharacterIterator with 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

    • parseObject

      public abstract Object parseObject(String source,ParsePosition pos)
      Parses text from the given string to produce an object.

      This method attempts to parse text starting at the index given bypos. If parsing succeeds, then the index ofpos 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 updatedpos can be used to indicate the starting point for the next call to this method. If an error occurs, then the index ofpos is not changed, the error index ofpos is set to the index of the character where the error occurred, andnull is returned.

      Parameters:
      source - theString to parse
      pos - AParsePosition object with index and error index information as described above.
      Returns:
      AnObject parsed from the string. In case of error, returnsnull.
      Throws:
      NullPointerException - ifsource orpos isnull.

    • parseObject

      public Object parseObject(String source) throwsParseException
      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:
      AnObject parsed from the string.
      Throws:
      ParseException - if parsing fails
      NullPointerException - ifsource isnull.

    • clone

      public Object clone()
      Creates and returns a copy of this object.
      Overrides:
      clone in class Object
      Returns:
      a clone of this instance.
      See Also: