decimalformat.java

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/*
 * @(#)DecimalFormat.java	1.71 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.InvalidObjectException;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Currency;
import java.util.Hashtable;
import java.util.Locale;
import java.util.ResourceBundle;
import sun.text.resources.LocaleData;

/**
 * <code>DecimalFormat</code> is a concrete subclass of
 * <code>NumberFormat</code> that formats decimal numbers. It has a variety of
 * features designed to make it possible to parse and format numbers in any
 * locale, including support for Western, Arabic, and Indic digits.  It also
 * supports different kinds of numbers, including integers (123), fixed-point
 * numbers (123.4), scientific notation (1.23E4), percentages (12%), and
 * currency amounts ($123).  All of these can be localized.
 *
 * <p>To obtain a <code>NumberFormat</code> for a specific locale, including the
 * default locale, call one of <code>NumberFormat</code>'s factory methods, such
 * as <code>getInstance()</code>.  In general, do not call the
 * <code>DecimalFormat</code> constructors directly, since the
 * <code>NumberFormat</code> factory methods may return subclasses other than
 * <code>DecimalFormat</code>. If you need to customize the format object, do
 * something like this:
 *
 * <blockquote><pre>
 * NumberFormat f = NumberFormat.getInstance(loc);
 * if (f instanceof DecimalFormat) {
 *     ((DecimalFormat) f).setDecimalSeparatorAlwaysShown(true);
 * }
 * </pre></blockquote>
 *
 * <p>A <code>DecimalFormat</code> comprises a <em>pattern</em> and a set of
 * <em>symbols</em>.  The pattern may be set directly using
 * <code>applyPattern()</code>, or indirectly using the API methods.  The
 * symbols are stored in a <code>DecimalFormatSymbols</code> object.  When using
 * the <code>NumberFormat</code> factory methods, the pattern and symbols are
 * read from localized <code>ResourceBundle</code>s.
 *
 * <h4>Patterns</h4>
 *
 * <code>DecimalFormat</code> patterns have the following syntax:
 * <blockquote><pre>
 * <i>Pattern:</i>
 *         <i>PositivePattern</i>
 *         <i>PositivePattern</i> ; <i>NegativePattern</i>
 * <i>PositivePattern:</i>
 *         <i>Prefix<sub>opt</sub></i> <i>Number</i> <i>Suffix<sub>opt</sub></i>
 * <i>NegativePattern:</i>
 *         <i>Prefix<sub>opt</sub></i> <i>Number</i> <i>Suffix<sub>opt</sub></i>
 * <i>Prefix:</i>
 *         any Unicode characters except &#92;uFFFE, &#92;uFFFF, and special characters
 * <i>Suffix:</i>
 *         any Unicode characters except &#92;uFFFE, &#92;uFFFF, and special characters
 * <i>Number:</i>
 *         <i>Integer</i> <i>Exponent<sub>opt</sub></i>
 *         <i>Integer</i> . <i>Fraction</i> <i>Exponent<sub>opt</sub></i>
 * <i>Integer:</i>
 *         <i>MinimumInteger</i>
 *         #
 *         # <i>Integer</i>
 *         # , <i>Integer</i>
 * <i>MinimumInteger:</i>
 *         0
 *         0 <i>MinimumInteger</i>
 *         0 , <i>MinimumInteger</i>
 * <i>Fraction:</i>
 *         <i>MinimumFraction<sub>opt</sub></i> <i>OptionalFraction<sub>opt</sub></i>
 * <i>MinimumFraction:</i>
 *         0 <i>MinimumFraction<sub>opt</sub></i>
 * <i>OptionalFraction:</i>
 *         # <i>OptionalFraction<sub>opt</sub></i>
 * <i>Exponent:</i>
 *         E <i>MinimumExponent</i>
 * <i>MinimumExponent:</i>
 *         0 <i>MinimumExponent<sub>opt</sub></i>
 * </pre></blockquote>
 *
 * <p>A <code>DecimalFormat</code> pattern contains a positive and negative
 * subpattern, for example, <code>"#,##0.00;(#,##0.00)"</code>.  Each
 * subpattern has a prefix, numeric part, and suffix. The negative subpattern
 * is optional; if absent, then the positive subpattern prefixed with the
 * localized minus sign (code>'-'</code> in most locales) is used as the
 * negative subpattern. That is, <code>"0.00"</code> alone is equivalent to
 * <code>"0.00;-0.00"</code>.  If there is an explicit negative subpattern, it
 * serves only to specify the negative prefix and suffix; the number of digits,
 * minimal digits, and other characteristics are all the same as the positive
 * pattern. That means that <code>"#,##0.0#;(#)"</code> produces precisely
 * the same behavior as <code>"#,##0.0#;(#,##0.0#)"</code>.
 *
 * <p>The prefixes, suffixes, and various symbols used for infinity, digits,
 * thousands separators, decimal separators, etc. may be set to arbitrary
 * values, and they will appear properly during formatting.  However, care must
 * be taken that the symbols and strings do not conflict, or parsing will be
 * unreliable.  For example, either the positive and negative prefixes or the
 * suffixes must be distinct for <code>DecimalFormat.parse()</code> to be able
 * to distinguish positive from negative values.  (If they are identical, then
 * <code>DecimalFormat</code> will behave as if no negative subpattern was
 * specified.)  Another example is that the decimal separator and thousands
 * separator should be distinct characters, or parsing will be impossible.
 *
 * <p>The grouping separator is commonly used for thousands, but in some
 * countries it separates ten-thousands. The grouping size is a constant number
 * of digits between the grouping characters, such as 3 for 100,000,000 or 4 for
 * 1,0000,0000.  If you supply a pattern with multiple grouping characters, the
 * interval between the last one and the end of the integer is the one that is
 * used. So <code>"#,##,###,####"</code> == <code>"######,####"</code> ==
 * <code>"##,####,####"</code>.
 *
 * <h4>Special Pattern Characters</h4>
 *
 * <p>Many characters in a pattern are taken literally; they are matched during
 * parsing and output unchanged during formatting.  Special characters, on the
 * other hand, stand for other characters, strings, or classes of characters.
 * They must be quoted, unless noted otherwise, if they are to appear in the
 * prefix or suffix as literals.
 *
 * <p>The characters listed here are used in non-localized patterns.  Localized
 * patterns use the corresponding characters taken from this formatter's
 * <code>DecimalFormatSymbols</code> object instead, and these characters lose
 * their special status.  Two exceptions are the currency sign and quote, which
 * are not localized.
 *
 * <blockquote>
 * <table border=0 cellspacing=3 cellpadding=0 summary="Chart showing symbol,
 *  location, localized, and meaning.">
 *     <tr bgcolor="#ccccff">
 *          <th align=left>Symbol
 *          <th align=left>Location
 *          <th align=left>Localized?
 *          <th align=left>Meaning
 *     <tr valign=top>
 *          <td><code>0</code>
 *          <td>Number
 *          <td>Yes
 *          <td>Digit
 *     <tr valign=top bgcolor="#eeeeff">
 *          <td><code>#</code>
 *          <td>Number
 *          <td>Yes
 *          <td>Digit, zero shows as absent
 *     <tr valign=top>
 *          <td><code>.</code>
 *          <td>Number
 *          <td>Yes
 *          <td>Decimal separator or monetary decimal separator
 *     <tr valign=top bgcolor="#eeeeff">
 *          <td><code>-</code>
 *          <td>Number
 *          <td>Yes
 *          <td>Minus sign
 *     <tr valign=top>
 *          <td><code>,</code>
 *          <td>Number
 *          <td>Yes
 *          <td>Grouping separator
 *     <tr valign=top bgcolor="#eeeeff">
 *          <td><code>E</code>
 *          <td>Number
 *          <td>Yes
 *          <td>Separates mantissa and exponent in scientific notation.
 *              <em>Need not be quoted in prefix or suffix.</em>
 *     <tr valign=top>
 *          <td><code>;</code>
 *          <td>Subpattern boundary
 *          <td>Yes
 *          <td>Separates positive and negative subpatterns
 *     <tr valign=top bgcolor="#eeeeff">
 *          <td><code>%</code>
 *          <td>Prefix or suffix
 *          <td>Yes
 *          <td>Multiply by 100 and show as percentage
 *     <tr valign=top>
 *          <td><code>&#92;u2030</code>
 *          <td>Prefix or suffix
 *          <td>Yes
 *          <td>Multiply by 1000 and show as per mille
 *     <tr valign=top bgcolor="#eeeeff">
 *          <td><code>&#164;</code> (<code>&#92;u00A4</code>)
 *          <td>Prefix or suffix
 *          <td>No
 *          <td>Currency sign, replaced by currency symbol.  If
 *              doubled, replaced by international currency symbol.
 *              If present in a pattern, the monetary decimal separator
 *              is used instead of the decimal separator.
 *     <tr valign=top>
 *          <td><code>'</code>
 *          <td>Prefix or suffix
 *          <td>No
 *          <td>Used to quote special characters in a prefix or suffix,
 *              for example, <code>"'#'#"</code> formats 123 to
 *              <code>"#123"</code>.  To create a single quote
 *              itself, use two in a row: <code>"# o''clock"</code>.
 * </table>
 * </blockquote>
 *
 * <h4>Scientific Notation</h4>
 *
 * <p>Numbers in scientific notation are expressed as the product of a mantissa
 * and a power of ten, for example, 1234 can be expressed as 1.234 x 10^3.  The
 * mantissa is often in the range 1.0 <= x < 10.0, but it need not be.
 * <code>DecimalFormat</code> can be instructed to format and parse scientific
 * notation <em>only via a pattern</em>; there is currently no factory method
 * that creates a scientific notation format.  In a pattern, the exponent
 * character immediately followed by one or more digit characters indicates
 * scientific notation.  Example: <code>"0.###E0"</code> formats the number
 * 1234 as <code>"1.234E3"</code>.
 *
 * <ul>
 * <li>The number of digit characters after the exponent character gives the
 * minimum exponent digit count.  There is no maximum.  Negative exponents are
 * formatted using the localized minus sign, <em>not</em> the prefix and suffix
 * from the pattern.  This allows patterns such as <code>"0.###E0 m/s"</code>.
 *
 * <li>The minimum and maximum number of integer digits are interpreted
 * together:
 *
 * <ul>
 * <li>If the maximum number of integer digits is greater than their minimum number
 * and greater than 1, it forces the exponent to be a multiple of the maximum
 * number of integer digits, and the minimum number of integer digits to be
 * interpreted as 1.  The most common use of this is to generate
 * <em>engineering notation</em>, in which the exponent is a multiple of three,
 * e.g., <code>"##0.#####E0"</code>. Using this pattern, the number 12345
 * formats to <code>"12.345E3"</code>, and 123456 formats to
 * <code>"123.456E3"</code>.
 *
 * <li>Otherwise, the minimum number of integer digits is achieved by adjusting the
 * exponent.  Example: 0.00123 formatted with <code>"00.###E0"</code> yields
 * <code>"12.3E-4"</code>.
 * </ul>
 *
 * <li>The number of significant digits in the mantissa is the sum of the
 * <em>minimum integer</em> and <em>maximum fraction</em> digits, and is
 * unaffected by the maximum integer digits.  For example, 12345 formatted with
 * <code>"##0.##E0"</code> is <code>"12.3E3"</code>. To show all digits, set
 * the significant digits count to zero.  The number of significant digits
 * does not affect parsing.
 *
 * <li>Exponential patterns may not contain grouping separators.
 * </ul>
 *
 * <h4>Rounding</h4>
 *
 * <code>DecimalFormat</code> uses half-even rounding (see
 * {@link java.math.BigDecimal#ROUND_HALF_EVEN ROUND_HALF_EVEN}) for
 * formatting.
 *
 * <h4>Digits</h4>
 *
 * For formatting, <code>DecimalFormat</code> uses the ten consecutive
 * characters starting with the localized zero digit defined in the
 * <code>DecimalFormatSymbols</code> object as digits. For parsing, these
 * digits as well as all Unicode decimal digits, as defined by
 * {@link Character#digit Character.digit}, are recognized.
 *
 * <h4>Special Values</h4>
 *
 * <p><code>NaN</code> is formatted as a single character, typically
 * <code>&#92;uFFFD</code>.  This character is determined by the
 * <code>DecimalFormatSymbols</code> object.  This is the only value for which
 * the prefixes and suffixes are not used.
 *
 * <p>Infinity is formatted as a single character, typically
 * <code>&#92;u221E</code>, with the positive or negative prefixes and suffixes
 * applied.  The infinity character is determined by the
 * <code>DecimalFormatSymbols</code> object.
 *
 * <p>Negative zero (<code>"-0"</code>) parses to <code>Double(-0.0)</code>,
 * unless <code>isParseIntegerOnly()</code> is true, in which case it parses to
 * <code>Long(0)</code>.
 *
 * <h4><a name="synchronization">Synchronization</a></h4>
 *
 * <p>
 * Decimal 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.
 *
 * <h4>Example</h4>
 *
 * <blockquote><pre>
 * <strong>// Print out a number using the localized number, integer, currency,
 * // and percent format for each locale</strong>
 * Locale[] locales = NumberFormat.getAvailableLocales();
 * double myNumber = -1234.56;
 * NumberFormat form;
 * for (int j=0; j<4; ++j) {
 *     System.out.println("FORMAT");
 *     for (int i = 0; i < locales.length; ++i) {