dateformat.java

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/*
 * @(#)DateFormat.java	1.47 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 - All Rights Reserved
 * (C) Copyright IBM Corp. 1996 - 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.InvalidObjectException;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
import java.util.ResourceBundle;
import java.util.MissingResourceException;
import java.util.TimeZone;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.Date;
import sun.text.resources.LocaleData;

/**
 * DateFormat is an abstract class for date/time formatting subclasses which
 * formats and parses dates or time in a language-independent manner.
 * The date/time formatting subclass, such as SimpleDateFormat, allows for
 * formatting (i.e., date -> text), parsing (text -> date), and
 * normalization.  The date is represented as a <code>Date</code> object or
 * as the milliseconds since January 1, 1970, 00:00:00 GMT.
 *
 * <p>DateFormat provides many class methods for obtaining default date/time
 * formatters based on the default or a given locale and a number of formatting
 * styles. The formatting styles include FULL, LONG, MEDIUM, and SHORT. More
 * detail and examples of using these styles are provided in the method
 * descriptions.
 *
 * <p>DateFormat helps you to format and parse dates for any locale.
 * Your code can be completely independent of the locale conventions for
 * months, days of the week, or even the calendar format: lunar vs. solar.
 *
 * <p>To format a date for the current Locale, use one of the
 * static factory methods:
 * <pre>
 *  myString = DateFormat.getDateInstance().format(myDate);
 * </pre>
 * <p>If you are formatting multiple dates, it is
 * more efficient to get the format and use it multiple times so that
 * the system doesn't have to fetch the information about the local
 * language and country conventions multiple times.
 * <pre>
 *  DateFormat df = DateFormat.getDateInstance();
 *  for (int i = 0; i < a.length; ++i) {
 *    output.println(df.format(myDate[i]) + "; ");
 *  }
 * </pre>
 * <p>To format a date for a different Locale, specify it in the
 * call to getDateInstance().
 * <pre>
 *  DateFormat df = DateFormat.getDateInstance(DateFormat.LONG, Locale.FRANCE);
 * </pre>
 * <p>You can use a DateFormat to parse also.
 * <pre>
 *  myDate = df.parse(myString);
 * </pre>
 * <p>Use getDateInstance to get the normal date format for that country.
 * There are other static factory methods available.
 * Use getTimeInstance to get the time format for that country.
 * Use getDateTimeInstance to get a date and time format. You can pass in 
 * different options to these factory methods to control the length of the
 * result; from SHORT to MEDIUM to LONG to FULL. The exact result depends
 * on the locale, but generally:
 * <ul><li>SHORT is completely numeric, such as 12.13.52 or 3:30pm
 * <li>MEDIUM is longer, such as Jan 12, 1952
 * <li>LONG is longer, such as January 12, 1952 or 3:30:32pm
 * <li>FULL is pretty completely specified, such as
 * Tuesday, April 12, 1952 AD or 3:30:42pm PST.
 * </ul>
 *
 * <p>You can also set the time zone on the format if you wish.
 * If you want even more control over the format or parsing,
 * (or want to give your users more control),
 * you can try casting the DateFormat you get from the factory methods
 * to a SimpleDateFormat. This will work for the majority
 * of countries; just remember to put it in a try block in case you
 * encounter an unusual one.
 *
 * <p>You can also use forms of the parse and format methods with
 * ParsePosition and FieldPosition to
 * allow you to
 * <ul><li>progressively parse through pieces of a string.
 * <li>align any particular field, or find out where it is for selection
 * on the screen.
 * </ul>
 *
 * <h4><a name="synchronization">Synchronization</a></h4>
 *
 * <p>
 * Date formats are 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          Format
 * @see          NumberFormat
 * @see          SimpleDateFormat
 * @see          java.util.Calendar
 * @see          java.util.GregorianCalendar
 * @see          java.util.TimeZone
 * @version      1.47 01/23/03
 * @author       Mark Davis, Chen-Lieh Huang, Alan Liu
 */
public abstract class DateFormat extends Format {

    /**
     * The calendar that <code>DateFormat</code> uses to produce the time field
     * values needed to implement date and time formatting.  Subclasses should
     * initialize this to a calendar appropriate for the locale associated with
     * this <code>DateFormat</code>.
     * @serial
     */
    protected Calendar calendar;

    /**
     * The number formatter that <code>DateFormat</code> uses to format numbers
     * in dates and times.  Subclasses should initialize this to a number format
     * appropriate for the locale associated with this <code>DateFormat</code>.
     * @serial
     */
    protected NumberFormat numberFormat;

    /**
     * Useful constant for ERA field alignment.
     * Used in FieldPosition of date/time formatting.
     */
    public final static int ERA_FIELD = 0;
    /**
     * Useful constant for YEAR field alignment.
     * Used in FieldPosition of date/time formatting.
     */
    public final static int YEAR_FIELD = 1;
    /**
     * Useful constant for MONTH field alignment.
     * Used in FieldPosition of date/time formatting.
     */
    public final static int MONTH_FIELD = 2;
    /**
     * Useful constant for DATE field alignment.
     * Used in FieldPosition of date/time formatting.
     */
    public final static int DATE_FIELD = 3;
    /**
     * Useful constant for one-based HOUR_OF_DAY field alignment.
     * Used in FieldPosition of date/time formatting.
     * HOUR_OF_DAY1_FIELD is used for the one-based 24-hour clock.
     * For example, 23:59 + 01:00 results in 24:59.
     */
    public final static int HOUR_OF_DAY1_FIELD = 4;
    /**
     * Useful constant for zero-based HOUR_OF_DAY field alignment.
     * Used in FieldPosition of date/time formatting.
     * HOUR_OF_DAY0_FIELD is used for the zero-based 24-hour clock.
     * For example, 23:59 + 01:00 results in 00:59.
     */
    public final static int HOUR_OF_DAY0_FIELD = 5;
    /**
     * Useful constant for MINUTE field alignment.
     * Used in FieldPosition of date/time formatting.
     */
    public final static int MINUTE_FIELD = 6;
    /**
     * Useful constant for SECOND field alignment.
     * Used in FieldPosition of date/time formatting.
     */
    public final static int SECOND_FIELD = 7;
    /**
     * Useful constant for MILLISECOND field alignment.
     * Used in FieldPosition of date/time formatting.
     */
    public final static int MILLISECOND_FIELD = 8;
    /**
     * Useful constant for DAY_OF_WEEK field alignment.
     * Used in FieldPosition of date/time formatting.
     */
    public final static int DAY_OF_WEEK_FIELD = 9;
    /**
     * Useful constant for DAY_OF_YEAR field alignment.
     * Used in FieldPosition of date/time formatting.
     */
    public final static int DAY_OF_YEAR_FIELD = 10;
    /**
     * Useful constant for DAY_OF_WEEK_IN_MONTH field alignment.
     * Used in FieldPosition of date/time formatting.
     */
    public final static int DAY_OF_WEEK_IN_MONTH_FIELD = 11;
    /**
     * Useful constant for WEEK_OF_YEAR field alignment.
     * Used in FieldPosition of date/time formatting.
     */
    public final static int WEEK_OF_YEAR_FIELD = 12;
    /**
     * Useful constant for WEEK_OF_MONTH field alignment.
     * Used in FieldPosition of date/time formatting.
     */
    public final static int WEEK_OF_MONTH_FIELD = 13;
    /**
     * Useful constant for AM_PM field alignment.
     * Used in FieldPosition of date/time formatting.
     */
    public final static int AM_PM_FIELD = 14;
    /**
     * Useful constant for one-based HOUR field alignment.
     * Used in FieldPosition of date/time formatting.
     * HOUR1_FIELD is used for the one-based 12-hour clock.
     * For example, 11:30 PM + 1 hour results in 12:30 AM.
     */
    public final static int HOUR1_FIELD = 15;
    /**
     * Useful constant for zero-based HOUR field alignment.
     * Used in FieldPosition of date/time formatting.
     * HOUR0_FIELD is used for the zero-based 12-hour clock.
     * For example, 11:30 PM + 1 hour results in 00:30 AM.
     */
    public final static int HOUR0_FIELD = 16;
    /**
     * Useful constant for TIMEZONE field alignment.
     * Used in FieldPosition of date/time formatting.
     */
    public final static int TIMEZONE_FIELD = 17;

    // Proclaim serial compatibility with 1.1 FCS
    private static final long serialVersionUID = 7218322306649953788L;

    /**
     * Overrides Format.
     * Formats a time object into a time string. Examples of time objects
     * are a time value expressed in milliseconds and a Date object.
     * @param obj must be a Number or a Date.
     * @param toAppendTo the string buffer for the returning time string.
     * @return the formatted time string.
     * @param fieldPosition keeps track of the position of the field
     * within the returned string.
     * On input: an alignment field,
     * if desired. On output: the offsets of the alignment field. For
     * example, given a time text "1996.07.10 AD at 15:08:56 PDT",
     * if the given fieldPosition is DateFormat.YEAR_FIELD, the
     * begin index and end index of fieldPosition will be set to
     * 0 and 4, respectively.
     * Notice that if the same time field appears
     * more than once in a pattern, the fieldPosition will be set for the first
     * occurrence of that time field. For instance, formatting a Date to
     * the time string "1 PM PDT (Pacific Daylight Time)" using the pattern
     * "h a z (zzzz)" and the alignment field DateFormat.TIMEZONE_FIELD,
     * the begin index and end index of fieldPosition will be set to
     * 5 and 8, respectively, for the first occurrence of the timezone
     * pattern character 'z'.
     * @see java.text.Format
     */
    public final StringBuffer format(Object obj, StringBuffer toAppendTo,
                                     FieldPosition fieldPosition)
    {
        if (obj instanceof Date)
            return format( (Date)obj, toAppendTo, fieldPosition );
        else if (obj instanceof Number)
            return format( new Date(((Number)obj).longValue()),
                          toAppendTo, fieldPosition );
        else 
            throw new IllegalArgumentException("Cannot format given Object as a Date");
    }

    /**
     * Formats a Date into a date/time string.
     * @param date a Date to be formatted into a date/time string.
     * @param toAppendTo the string buffer for the returning date/time string.
     * @param fieldPosition keeps track of the position of the field
     * within the returned string.
     * On input: an alignment field,
     * if desired. On output: the offsets of the alignment field. For
     * example, given a time text "1996.07.10 AD at 15:08:56 PDT",
     * if the given fieldPosition is DateFormat.YEAR_FIELD, the
     * begin index and end index of fieldPosition will be set to
     * 0 and 4, respectively.
     * Notice that if the same time field appears
     * more than once in a pattern, the fieldPosition will be set for the first
     * occurrence of that time field. For instance, formatting a Date to
     * the time string "1 PM PDT (Pacific Daylight Time)" using the pattern
     * "h a z (zzzz)" and the alignment field DateFormat.TIMEZONE_FIELD,
     * the begin index and end index of fieldPosition will be set to
     * 5 and 8, respectively, for the first occurrence of the timezone