format.java

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/*
 * @(#)Format.java	1.32 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

/*
 * (C) Copyright Taligent, Inc. 1996, 1997 - All Rights Reserved
 * (C) Copyright IBM Corp. 1996 - 1998 - All Rights Reserved
 *
 *   The original version of this source code and documentation is copyrighted
 * and owned by Taligent, Inc., a wholly-owned subsidiary of IBM. These
 * materials are provided under terms of a License Agreement between Taligent
 * and Sun. This technology is protected by multiple US and International
 * patents. This notice and attribution to Taligent may not be removed.
 *   Taligent is a registered trademark of Taligent, Inc.
 *
 */

package java.text;

import java.io.Serializable;

/**
 * <code>Format</code> is an abstract base class for formatting locale-sensitive
 * information such as dates, messages, and numbers.
 *
 * <p>
 * <code>Format</code> defines the programming interface for formatting
 * locale-sensitive objects into <code>String</code>s (the
 * <code>format</code> method) and for parsing <code>String</code>s back
 * into objects (the <code>parseObject</code> method).
 *
 * <p>
 * Generally, a format's <code>parseObject</code> method must be able to parse
 * any string formatted by its <code>format</code> method. However, there may 
 * be exceptional cases where this is not possible. For example, a
 * <code>format</code> method might create two adjacent integer numbers with
 * no separator in between, and in this case the <code>parseObject</code> could
 * not tell which digits belong to which number.
 *
 * <h4>Subclassing</h4>
 *
 * <p>
 * The Java 2 platform provides three specialized subclasses of <code>Format</code>--
 * <code>DateFormat</code>, <code>MessageFormat</code>, and
 * <code>NumberFormat</code>--for formatting dates, messages, and numbers,
 * respectively.
 * <p>
 * Concrete subclasses must implement three methods:
 * <ol>
 * <li> <code>format(Object obj, StringBuffer toAppendTo, FieldPosition pos)</code>
 * <li> <code>formatToCharacterIterator(Object obj)</code>
 * <li> <code>parseObject(String source, ParsePosition pos)</code>
 * </ol>
 * These general methods allow polymorphic parsing and formatting of objects
 * and are used, for example, by <code>MessageFormat</code>.
 * Subclasses often also provide additional <code>format</code> methods for
 * specific input types as well as <code>parse</code> methods for specific
 * result types. Any <code>parse</code> method that does not take a
 * <code>ParsePosition</code> argument should throw <code>ParseException</code>
 * when no text in the required format is at the beginning of the input text.
 *
 * <p>
 * Most subclasses will also implement the following factory methods:
 * <ol>
 * <li>
 * <code>getInstance</code> for getting a useful format object appropriate
 * for the current locale
 * <li>
 * <code>getInstance(Locale)</code> for getting a useful format
 * object appropriate for the specified locale
 * </ol>
 * In addition, some subclasses may also implement other
 * <code>getXxxxInstance</code> methods for more specialized control. For
 * example, the <code>NumberFormat</code> class provides
 * <code>getPercentInstance</code> and <code>getCurrencyInstance</code>
 * methods for getting specialized number formatters.
 *
 * <p>
 * Subclasses of <code>Format</code> that allow programmers to create objects
 * for locales (with <code>getInstance(Locale)</code> for example)
 * must also implement the following class method:
 * <blockquote>
 * <pre>
 * public static Locale[] getAvailableLocales()
 * </pre>
 * </blockquote>
 *
 * <p>
 * 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
 * <code><em>item</em>_FIELD</code> where <code><em>item</em></code> identifies
 * the field. For examples of these constants, see <code>ERA_FIELD</code> and its
 * friends in {@link DateFormat}.
 *
 * <h4><a name="synchronization">Synchronization</a></h4>
 *
 * <p>
 * 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
 * @version      1.32, 01/23/03
 * @author       Mark Davis
 */
public abstract class Format implements Serializable, Cloneable {

    private static final long serialVersionUID = -299282585814624189L;

    /**
     * Formats an object to produce a string. This is equivalent to
     * <blockquote>
     * {@link #format(Object, StringBuffer, FieldPosition) format}<code>(obj,
     *         new StringBuffer(), new FieldPosition(0)).toString();</code>
     * </blockquote>
     *
     * @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 <code>pos</code> 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 <code>FieldPosition</code> identifying a field
     *               in the formatted text
     * @return       the string buffer passed in as <code>toAppendTo</code>,
     *               with formatted text appended
     * @exception NullPointerException if <code>toAppendTo</code> or
     *            <code>pos</code> 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 <code>AttributedCharacterIterator</code>.
     * You can use the returned <code>AttributedCharacterIterator</code>
     * to build the resulting String, as well as to determine information
     * about the resulting String.
     * <p>
     * Each attribute key of the AttributedCharacterIterator will be of type
     * <code>Field</code>. It is up to each <code>Format</code> implementation
     * to define what the legal values are for each attribute in the
     * <code>AttributedCharacterIterator</code>, but typically the attribute
     * key is also used as the attribute value.
     * <p>The default implementation creates an
     * <code>AttributedCharacterIterator</code> with no attributes. Subclasses
     * that support fields should override this and create an
     * <code>AttributedCharacterIterator</code> 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.
     * <p>
     * The method attempts to parse text starting at the index given by
     * <code>pos</code>.
     * If parsing succeeds, then the index of <code>pos</code> is updated