Module java.base
Package java.text

Class Format

  • All Implemented Interfaces:
    Serializable,Cloneable
    Direct Known Subclasses:
    DateFormat,MessageFormat,NumberFormat
    public abstract classFormatextendsObjectimplementsSerializable,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 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 three specialized subclasses ofFormat--DateFormat,MessageFormat, andNumberFormat--for formatting dates, messages, and numbers, 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()

    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:
    ParsePosition,FieldPosition,NumberFormat,DateFormat,MessageFormat,Serialized Form

    • 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 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.

        The default implementation creates anAttributedCharacterIterator with no attributes. Subclasses that support fields should override this and create anAttributedCharacterIterator 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 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, 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:
        AnObject parsed from the string. In case of error, returns null.
        Throws:
        NullPointerException - ifsource orpos is null.

      • parseObject

        public Object parseObject​(String source)                   throwsParseException
        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:
        AnObject 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.
        Overrides:
        clone in class Object
        Returns:
        a clone of this instance.
        See Also:
        Cloneable