/*

 * Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.nio.charset;

import java.nio.ByteBuffer;

import java.nio.CharBuffer;

import java.nio.charset.spi.CharsetProvider;

import java.security.AccessController;

import java.security.AccessControlException;

import java.security.PrivilegedAction;

import java.util.Collections;

import java.util.HashSet;

import java.util.Iterator;

import java.util.Locale;

import java.util.Map;

import java.util.NoSuchElementException;

import java.util.Set;

import java.util.ServiceLoader;

import java.util.ServiceConfigurationError;

import java.util.SortedMap;

import java.util.TreeMap;

import sun.misc.ASCIICaseInsensitiveComparator;

import sun.nio.cs.StandardCharsets;

import sun.nio.cs.ThreadLocalCoders;

import sun.security.action.GetPropertyAction;

/**

 * A named mapping between sequences of sixteen-bit Unicode <a

 * href="../../lang/Character.html#unicode">code units</a> and sequences of

 * bytes.  This class defines methods for creating decoders and encoders and

 * for retrieving the various names associated with a charset.  Instances of

 * this class are immutable.

 *

 * <p> This class also defines static methods for testing whether a particular

 * charset is supported, for locating charset instances by name, and for

 * constructing a map that contains every charset for which support is

 * available in the current Java virtual machine.  Support for new charsets can

 * be added via the service-provider interface defined in the {@link

 * java.nio.charset.spi.CharsetProvider} class.

 *

 * <p> All of the methods defined in this class are safe for use by multiple

 * concurrent threads.

 *

 *

 * <a name="names"><a name="charenc">

 * <h4>Charset names</h4>

 *

 * <p> Charsets are named by strings composed of the following characters:

 *

 * <ul>

 *

 *   <li> The uppercase letters <tt>'A'</tt> through <tt>'Z'</tt>

 *        (<tt>'&#92;u0041'</tt>&nbsp;through&nbsp;<tt>'&#92;u005a'</tt>),

 *

 *   <li> The lowercase letters <tt>'a'</tt> through <tt>'z'</tt>

 *        (<tt>'&#92;u0061'</tt>&nbsp;through&nbsp;<tt>'&#92;u007a'</tt>),

 *

 *   <li> The digits <tt>'0'</tt> through <tt>'9'</tt>

 *        (<tt>'&#92;u0030'</tt>&nbsp;through&nbsp;<tt>'&#92;u0039'</tt>),

 *

 *   <li> The dash character <tt>'-'</tt>

 *        (<tt>'&#92;u002d'</tt>,&nbsp;<small>HYPHEN-MINUS</small>),

 *

 *   <li> The plus character <tt>'+'</tt>

 *        (<tt>'&#92;u002b'</tt>,&nbsp;<small>PLUS SIGN</small>),

 *

 *   <li> The period character <tt>'.'</tt>

 *        (<tt>'&#92;u002e'</tt>,&nbsp;<small>FULL STOP</small>),

 *

 *   <li> The colon character <tt>':'</tt>

 *        (<tt>'&#92;u003a'</tt>,&nbsp;<small>COLON</small>), and

 *

 *   <li> The underscore character <tt>'_'</tt>

 *        (<tt>'&#92;u005f'</tt>,&nbsp;<small>LOW&nbsp;LINE</small>).

 *

 * </ul>

 *

 * A charset name must begin with either a letter or a digit.  The empty string

 * is not a legal charset name.  Charset names are not case-sensitive; that is,

 * case is always ignored when comparing charset names.  Charset names

 * generally follow the conventions documented in <a

 * href="http://www.ietf.org/rfc/rfc2278.txt"><i>RFC&nbsp;2278:&nbsp;IANA Charset

 * Registration Procedures</i></a>.

 *

 * <p> Every charset has a <i>canonical name</i> and may also have one or more

 * <i>aliases</i>.  The canonical name is returned by the {@link #name() name} method

 * of this class.  Canonical names are, by convention, usually in upper case.

 * The aliases of a charset are returned by the {@link #aliases() aliases}

 * method.

 *

 * <a name="hn">

 *

 * <p> Some charsets have an <i>historical name</i> that is defined for

 * compatibility with previous versions of the Java platform.  A charset's

 * historical name is either its canonical name or one of its aliases.  The

 * historical name is returned by the <tt>getEncoding()</tt> methods of the

 * {@link java.io.InputStreamReader#getEncoding InputStreamReader} and {@link

 * java.io.OutputStreamWriter#getEncoding OutputStreamWriter} classes.

 *

 * <a name="iana">

 *

 * <p> If a charset listed in the <a

 * href="http://www.iana.org/assignments/character-sets"><i>IANA Charset

 * Registry</i></a> is supported by an implementation of the Java platform then

 * its canonical name must be the name listed in the registry.  Many charsets

 * are given more than one name in the registry, in which case the registry

 * identifies one of the names as <i>MIME-preferred</i>.  If a charset has more

 * than one registry name then its canonical name must be the MIME-preferred

 * name and the other names in the registry must be valid aliases.  If a

 * supported charset is not listed in the IANA registry then its canonical name

 * must begin with one of the strings <tt>"X-"</tt> or <tt>"x-"</tt>.

 *

 * <p> The IANA charset registry does change over time, and so the canonical

 * name and the aliases of a particular charset may also change over time.  To

 * ensure compatibility it is recommended that no alias ever be removed from a

 * charset, and that if the canonical name of a charset is changed then its

 * previous canonical name be made into an alias.

 *

 *

 * <h4>Standard charsets</h4>

 *

 * <a name="standard">

 *

 * <p> Every implementation of the Java platform is required to support the

 * following standard charsets.  Consult the release documentation for your

 * implementation to see if any other charsets are supported.  The behavior

 * of such optional charsets may differ between implementations.

 *

 * <blockquote><table width="80%" summary="Description of standard charsets">

 * <tr><th><p align="left">Charset</p></th><th><p align="left">Description</p></th></tr>

 * <tr><td valign=top><tt>US-ASCII</tt></td>

 *     <td>Seven-bit ASCII, a.k.a. <tt>ISO646-US</tt>,

 *         a.k.a. the Basic Latin block of the Unicode character set</td></tr>

 * <tr><td valign=top><tt>ISO-8859-1&nbsp;&nbsp;</tt></td>

 *     <td>ISO Latin Alphabet No. 1, a.k.a. <tt>ISO-LATIN-1</tt></td></tr>

 * <tr><td valign=top><tt>UTF-8</tt></td>

 *     <td>Eight-bit UCS Transformation Format</td></tr>

 * <tr><td valign=top><tt>UTF-16BE</tt></td>

 *     <td>Sixteen-bit UCS Transformation Format,

 *         big-endian byte&nbsp;order</td></tr>

 * <tr><td valign=top><tt>UTF-16LE</tt></td>

 *     <td>Sixteen-bit UCS Transformation Format,

 *         little-endian byte&nbsp;order</td></tr>

 * <tr><td valign=top><tt>UTF-16</tt></td>

 *     <td>Sixteen-bit UCS Transformation Format,

 *         byte&nbsp;order identified by an optional byte-order mark</td></tr>

 * </table></blockquote>

 *

 * <p> The <tt>UTF-8</tt> charset is specified by <a

 * href="http://www.ietf.org/rfc/rfc2279.txt"><i>RFC&nbsp;2279</i></a>; the

 * transformation format upon which it is based is specified in

 * Amendment&nbsp;2 of ISO&nbsp;10646-1 and is also described in the <a

 * href="http://www.unicode.org/unicode/standard/standard.html"><i>Unicode

 * Standard</i></a>.

 *

 * <p> The <tt>UTF-16</tt> charsets are specified by <a

 * href="http://www.ietf.org/rfc/rfc2781.txt"><i>RFC&nbsp;2781</i></a>; the

 * transformation formats upon which they are based are specified in

 * Amendment&nbsp;1 of ISO&nbsp;10646-1 and are also described in the <a

 * href="http://www.unicode.org/unicode/standard/standard.html"><i>Unicode

 * Standard</i></a>.

 *

 * <p> The <tt>UTF-16</tt> charsets use sixteen-bit quantities and are

 * therefore sensitive to byte order.  In these encodings the byte order of a

 * stream may be indicated by an initial <i>byte-order mark</i> represented by

 * the Unicode character <tt>'&#92;uFEFF'</tt>.  Byte-order marks are handled

 * as follows:

 *

 * <ul>

 *

 *   <li><p> When decoding, the <tt>UTF-16BE</tt> and <tt>UTF-16LE</tt>

 *   charsets interpret the initial byte-order marks as a <small>ZERO-WIDTH

 *   NON-BREAKING SPACE</small>; when encoding, they do not write

 *   byte-order marks. </p></li>

 *

 *   <li><p> When decoding, the <tt>UTF-16</tt> charset interprets the

 *   byte-order mark at the beginning of the input stream to indicate the

 *   byte-order of the stream but defaults to big-endian if there is no

 *   byte-order mark; when encoding, it uses big-endian byte order and writes

 *   a big-endian byte-order mark. </p></li>

 *

 * </ul>

 *

 * In any case, byte order marks occuring after the first element of an

 * input sequence are not omitted since the same code is used to represent

 * <small>ZERO-WIDTH NON-BREAKING SPACE</small>.

 *

 * <p> Every instance of the Java virtual machine has a default charset, which

 * may or may not be one of the standard charsets.  The default charset is

 * determined during virtual-machine startup and typically depends upon the

 * locale and charset being used by the underlying operating system. </p>

 *

 * <p>The {@link StandardCharsets} class defines constants for each of the

 * standard charsets.

 *

 * <h4>Terminology</h4>

 *

 * <p> The name of this class is taken from the terms used in

 * <a href="http://www.ietf.org/rfc/rfc2278.txt"><i>RFC&nbsp;2278</i></a>.

 * In that document a <i>charset</i> is defined as the combination of

 * one or more coded character sets and a character-encoding scheme.

 * (This definition is confusing; some other software systems define

 * <i>charset</i> as a synonym for <i>coded character set</i>.)

 *

 * <p> A <i>coded character set</i> is a mapping between a set of abstract

 * characters and a set of integers.  US-ASCII, ISO 8859-1,

 * JIS X 0201, and Unicode are examples of coded character sets.

 *

 * <p> Some standards have defined a <i>character set</i> to be simply a

 * set of abstract characters without an associated assigned numbering.

 * An alphabet is an example of such a character set.  However, the subtle

 * distinction between <i>character set</i> and <i>coded character set</i>

 * is rarely used in practice; the former has become a short form for the

 * latter, including in the Java API specification.

 *

 * <p> A <i>character-encoding scheme</i> is a mapping between one or more

 * coded character sets and a set of octet (eight-bit byte) sequences.

 * UTF-8, UTF-16, ISO 2022, and EUC are examples of

 * character-encoding schemes.  Encoding schemes are often associated with

 * a particular coded character set; UTF-8, for example, is used only to

 * encode Unicode.  Some schemes, however, are associated with multiple

 * coded character sets; EUC, for example, can be used to encode

 * characters in a variety of Asian coded character sets.

 *

 * <p> When a coded character set is used exclusively with a single

 * character-encoding scheme then the corresponding charset is usually

 * named for the coded character set; otherwise a charset is usually named

 * for the encoding scheme and, possibly, the locale of the coded

 * character sets that it supports.  Hence <tt>US-ASCII</tt> is both the

 * name of a coded character set and of the charset that encodes it, while

 * <tt>EUC-JP</tt> is the name of the charset that encodes the

 * JIS X 0201, JIS X 0208, and JIS X 0212

 * coded character sets for the Japanese language.

 *

 * <p> The native character encoding of the Java programming language is

 * UTF-16.  A charset in the Java platform therefore defines a mapping

 * between sequences of sixteen-bit UTF-16 code units (that is, sequences

 * of chars) and sequences of bytes. </p>

 *

 *

 * @author Mark Reinhold

 * @author JSR-51 Expert Group

 * @since 1.4

 *

 * @see CharsetDecoder

 * @see CharsetEncoder

 * @see java.nio.charset.spi.CharsetProvider

 * @see java.lang.Character

 */

public abstract class Charset

    implements Comparable<Charset>

{

    /* -- Static methods -- */

    private static volatile String bugLevel = null;

    static boolean atBugLevel(String bl) {              // package-private

        String level = bugLevel;

        if (level == null) {

            if (!sun.misc.VM.isBooted())

                return false;

            bugLevel = level = AccessController.doPrivileged(

                new GetPropertyAction("sun.nio.cs.bugLevel", ""));

        }

        return level.equals(bl);

    }

    /**

     * Checks that the given string is a legal charset name. </p>

     *

     * @param  s

     *         A purported charset name

     *

     * @throws  IllegalCharsetNameException

     *          If the given name is not a legal charset name

     */

    private static void checkName(String s) {

        int n = s.length();

        if (!atBugLevel("1.4")) {

            if (n == 0)

                throw new IllegalCharsetNameException(s);

        }

        for (int i = 0; i < n; i++) {

            char c = s.charAt(i);

            if (c >= 'A' && c <= 'Z') continue;

            if (c >= 'a' && c <= 'z') continue;

            if (c >= '0' && c <= '9') continue;

            if (c == '-' && i != 0) continue;

            if (c == '+' && i != 0) continue;

            if (c == ':' && i != 0) continue;

            if (c == '_' && i != 0) continue;

            if (c == '.' && i != 0) continue;

            throw new IllegalCharsetNameException(s);

        }

    }

    /* The standard set of charsets */

    private static CharsetProvider standardProvider = new StandardCharsets();

    // Cache of the most-recently-returned charsets,

    // along with the names that were used to find them

    //

    private static volatile Object[] cache1 = null; // "Level 1" cache

    private static volatile Object[] cache2 = null; // "Level 2" cache

    private static void cache(String charsetName, Charset cs) {

        cache2 = cache1;

        cache1 = new Object[] { charsetName, cs };

    }

    // Creates an iterator that walks over the available providers, ignoring

    // those whose lookup or instantiation causes a security exception to be

    // thrown.  Should be invoked with full privileges.

    //

    private static Iterator providers() {

        return new Iterator() {

                ClassLoader cl = ClassLoader.getSystemClassLoader();

                ServiceLoader<CharsetProvider> sl =

                    ServiceLoader.load(CharsetProvider.class, cl);

                Iterator<CharsetProvider> i = sl.iterator();

                Object next = null;

                private boolean getNext() {

                    while (next == null) {

                        try {

                            if (!i.hasNext())

                                return false;

                            next = i.next();

                        } catch (ServiceConfigurationError sce) {

                            if (sce.getCause() instanceof SecurityException) {

                                // Ignore security exceptions

                                continue;

                            }

                            throw sce;

                        }

                    }

                    return true;

                }

                public boolean hasNext() {

                    return getNext();

                }

                public Object next() {

                    if (!getNext())

                        throw new NoSuchElementException();

                    Object n = next;

                    next = null;

                    return n;

                }

                public void remove() {

                    throw new UnsupportedOperationException();

                }

            };

    }

    // Thread-local gate to prevent recursive provider lookups

    private static ThreadLocal<ThreadLocal> gate = new ThreadLocal<ThreadLocal>();

    private static Charset lookupViaProviders(final String charsetName) {

        // The runtime startup sequence looks up standard charsets as a

        // consequence of the VM's invocation of System.initializeSystemClass

        // in order to, e.g., set system properties and encode filenames.  At

        // that point the application class loader has not been initialized,

        // however, so we can't look for providers because doing so will cause

        // that loader to be prematurely initialized with incomplete

        // information.

        //

        if (!sun.misc.VM.isBooted())

            return null;

        if (gate.get() != null)

            // Avoid recursive provider lookups

            return null;

        try {

            gate.set(gate);

            return AccessController.doPrivileged(

                new PrivilegedAction<Charset>() {

                    public Charset run() {

                        for (Iterator i = providers(); i.hasNext();) {

                            CharsetProvider cp = (CharsetProvider)i.next();

                            Charset cs = cp.charsetForName(charsetName);

                            if (cs != null)

                                return cs;

                        }

                        return null;

                    }

                });

        } finally {

            gate.set(null);

        }

    }

    /* The extended set of charsets */

    private static Object extendedProviderLock = new Object();

    private static boolean extendedProviderProbed = false;

    private static CharsetProvider extendedProvider = null;

    private static void probeExtendedProvider() {

        AccessController.doPrivileged(new PrivilegedAction<Object>() {

                public Object run() {

                    try {

                        Class epc

                            = Class.forName("sun.nio.cs.ext.ExtendedCharsets");

                        extendedProvider = (CharsetProvider)epc.newInstance();

                    } catch (ClassNotFoundException x) {

                        // Extended charsets not available

                        // (charsets.jar not present)

                    } catch (InstantiationException x) {

                        throw new Error(x);

                    } catch (IllegalAccessException x) {

                        throw new Error(x);

                    }

                    return null;

                }

            });

    }

    private static Charset lookupExtendedCharset(String charsetName) {

        CharsetProvider ecp = null;

        synchronized (extendedProviderLock) {

            if (!extendedProviderProbed) {

                probeExtendedProvider();

                extendedProviderProbed = true;

            }

            ecp = extendedProvider;

        }

        return (ecp != null) ? ecp.charsetForName(charsetName) : null;

    }

    private static Charset lookup(String charsetName) {

        if (charsetName == null)

            throw new IllegalArgumentException("Null charset name");

        Object[] a;

        if ((a = cache1) != null && charsetName.equals(a[0]))

            return (Charset)a[1];

        // We expect most programs to use one Charset repeatedly.

        // We convey a hint to this effect to the VM by putting the

        // level 1 cache miss code in a separate method.

        return lookup2(charsetName);

    }

    private static Charset lookup2(String charsetName) {

        Object[] a;

        if ((a = cache2) != null && charsetName.equals(a[0])) {

            cache2 = cache1;

            cache1 = a;

            return (Charset)a[1];

        }

        Charset cs;

        if ((cs = standardProvider.charsetForName(charsetName)) != null ||

            (cs = lookupExtendedCharset(charsetName))           != null ||

            (cs = lookupViaProviders(charsetName))              != null)

        {

            cache(charsetName, cs);

            return cs;

        }

        /* Only need to check the name if we didn't find a charset for it */

        checkName(charsetName);

        return null;

    }

    /**

     * Tells whether the named charset is supported. </p>

     *

     * @param  charsetName

     *         The name of the requested charset; may be either

     *         a canonical name or an alias

     *

     * @return  <tt>true</tt> if, and only if, support for the named charset

     *          is available in the current Java virtual machine

     *

     * @throws IllegalCharsetNameException

     *         If the given charset name is illegal

     *

     * @throws  IllegalArgumentException

     *          If the given <tt>charsetName</tt> is null

     */

    public static boolean isSupported(String charsetName) {

        return (lookup(charsetName) != null);

    }

    /**

     * Returns a charset object for the named charset. </p>

     *

     * @param  charsetName

     *         The name of the requested charset; may be either

     *         a canonical name or an alias

     *

     * @return  A charset object for the named charset

     *

     * @throws  IllegalCharsetNameException

     *          If the given charset name is illegal

     *

     * @throws  IllegalArgumentException

     *          If the given <tt>charsetName</tt> is null

     *

     * @throws  UnsupportedCharsetException

     *          If no support for the named charset is available

     *          in this instance of the Java virtual machine

     */

    public static Charset forName(String charsetName) {

        Charset cs = lookup(charsetName);

        if (cs != null)

            return cs;

        throw new UnsupportedCharsetException(charsetName);

    }

    // Fold charsets from the given iterator into the given map, ignoring

    // charsets whose names already have entries in the map.

    //

    private static void put(Iterator<Charset> i, Map<String,Charset> m) {

        while (i.hasNext()) {

            Charset cs = i.next();

            if (!m.containsKey(cs.name()))

                m.put(cs.name(), cs);

        }

    }

    /**

     * Constructs a sorted map from canonical charset names to charset objects.

     *

     * <p> The map returned by this method will have one entry for each charset

     * for which support is available in the current Java virtual machine.  If

     * two or more supported charsets have the same canonical name then the

     * resulting map will contain just one of them; which one it will contain

     * is not specified. </p>

     *

     * <p> The invocation of this method, and the subsequent use of the

     * resulting map, may cause time-consuming disk or network I/O operations

     * to occur.  This method is provided for applications that need to

     * enumerate all of the available charsets, for example to allow user

     * charset selection.  This method is not used by the {@link #forName

     * forName} method, which instead employs an efficient incremental lookup

     * algorithm.

     *

     * <p> This method may return different results at different times if new

     * charset providers are dynamically made available to the current Java

     * virtual machine.  In the absence of such changes, the charsets returned

     * by this method are exactly those that can be retrieved via the {@link

     * #forName forName} method.  </p>

     *

     * @return An immutable, case-insensitive map from canonical charset names

     *         to charset objects

     */

    public static SortedMap<String,Charset> availableCharsets() {

        return AccessController.doPrivileged(

            new PrivilegedAction<SortedMap<String,Charset>>() {

                public SortedMap<String,Charset> run() {

                    TreeMap<String,Charset> m =

                        new TreeMap<String,Charset>(

                            ASCIICaseInsensitiveComparator.CASE_INSENSITIVE_ORDER);

                    put(standardProvider.charsets(), m);

                    for (Iterator i = providers(); i.hasNext();) {

                        CharsetProvider cp = (CharsetProvider)i.next();

                        put(cp.charsets(), m);

                    }

                    return Collections.unmodifiableSortedMap(m);

                }

            });

    }

    private static volatile Charset defaultCharset;

    /**

     * Returns the default charset of this Java virtual machine.

     *

     * <p> The default charset is determined during virtual-machine startup and

     * typically depends upon the locale and charset of the underlying

     * operating system.

     *

     * @return  A charset object for the default charset

     *

     * @since 1.5

     */

    public static Charset defaultCharset() {

        if (defaultCharset == null) {

            synchronized (Charset.class) {

                String csn = AccessController.doPrivileged(

                    new GetPropertyAction("file.encoding"));

                Charset cs = lookup(csn);

                if (cs != null)

                    defaultCharset = cs;

                else

                    defaultCharset = forName("UTF-8");

            }

        }

        return defaultCharset;

    }

    /* -- Instance fields and methods -- */

    private final String name;          // tickles a bug in oldjavac

    private final String[] aliases;     // tickles a bug in oldjavac

    private Set<String> aliasSet = null;

    /**

     * Initializes a new charset with the given canonical name and alias

     * set. </p>

     *

     * @param  canonicalName

     *         The canonical name of this charset

     *

     * @param  aliases

     *         An array of this charset's aliases, or null if it has no aliases

     *

     * @throws IllegalCharsetNameException

     *         If the canonical name or any of the aliases are illegal

     */

    protected Charset(String canonicalName, String[] aliases) {

        checkName(canonicalName);

        String[] as = (aliases == null) ? new String[0] : aliases;

        for (int i = 0; i < as.length; i++)

            checkName(as[i]);

        this.name = canonicalName;

        this.aliases = as;

    }

    /**

     * Returns this charset's canonical name. </p>

     *

     * @return  The canonical name of this charset

     */

    public final String name() {

        return name;

    }

    /**

     * Returns a set containing this charset's aliases. </p>

     *

     * @return  An immutable set of this charset's aliases

     */

    public final Set<String> aliases() {

        if (aliasSet != null)

            return aliasSet;

        int n = aliases.length;

        HashSet<String> hs = new HashSet<String>(n);

        for (int i = 0; i < n; i++)

            hs.add(aliases[i]);

        aliasSet = Collections.unmodifiableSet(hs);

        return aliasSet;

    }

    /**

     * Returns this charset's human-readable name for the default locale.

     *

     * <p> The default implementation of this method simply returns this

     * charset's canonical name.  Concrete subclasses of this class may

     * override this method in order to provide a localized display name. </p>

     *

     * @return  The display name of this charset in the default locale

     */

    public String displayName() {

        return name;

    }

    /**

     * Tells whether or not this charset is registered in the <a

     * href="http://www.iana.org/assignments/character-sets">IANA Charset

     * Registry</a>.  </p>

     *

     * @return  <tt>true</tt> if, and only if, this charset is known by its

     *          implementor to be registered with the IANA

     */

    public final boolean isRegistered() {

        return !name.startsWith("X-") && !name.startsWith("x-");

    }

    /**

     * Returns this charset's human-readable name for the given locale.

     *

     * <p> The default implementation of this method simply returns this

     * charset's canonical name.  Concrete subclasses of this class may

     * override this method in order to provide a localized display name. </p>

     *

     * @param  locale

     *         The locale for which the display name is to be retrieved

     *

     * @return  The display name of this charset in the given locale

     */

    public String displayName(Locale locale) {

        return name;

    }

    /**

     * Tells whether or not this charset contains the given charset.

     *

     * <p> A charset <i>C</i> is said to <i>contain</i> a charset <i>D</i> if,

     * and only if, every character representable in <i>D</i> is also

     * representable in <i>C</i>.  If this relationship holds then it is

     * guaranteed that every string that can be encoded in <i>D</i> can also be

     * encoded in <i>C</i> without performing any replacements.

     *

     * <p> That <i>C</i> contains <i>D</i> does not imply that each character

     * representable in <i>C</i> by a particular byte sequence is represented

     * in <i>D</i> by the same byte sequence, although sometimes this is the

     * case.

     *

     * <p> Every charset contains itself.

     *

     * <p> This method computes an approximation of the containment relation:

     * If it returns <tt>true</tt> then the given charset is known to be

     * contained by this charset; if it returns <tt>false</tt>, however, then

     * it is not necessarily the case that the given charset is not contained

     * in this charset.

     *

     * @return  <tt>true</tt> if the given charset is contained in this charset

     */

    public abstract boolean contains(Charset cs);

    /**

     * Constructs a new decoder for this charset. </p>

     *

     * @return  A new decoder for this charset

     */

    public abstract CharsetDecoder newDecoder();

    /**

     * Constructs a new encoder for this charset. </p>

     *

     * @return  A new encoder for this charset

     *

     * @throws  UnsupportedOperationException

     *          If this charset does not support encoding

     */

    public abstract CharsetEncoder newEncoder();

    /**

     * Tells whether or not this charset supports encoding.

     *

     * <p> Nearly all charsets support encoding.  The primary exceptions are

     * special-purpose <i>auto-detect</i> charsets whose decoders can determine

     * which of several possible encoding schemes is in use by examining the

     * input byte sequence.  Such charsets do not support encoding because

     * there is no way to determine which encoding should be used on output.

     * Implementations of such charsets should override this method to return

     * <tt>false</tt>. </p>

     *

     * @return  <tt>true</tt> if, and only if, this charset supports encoding

     */

    public boolean canEncode() {

        return true;

    }

    /**

     * Convenience method that decodes bytes in this charset into Unicode

     * characters.

     *

     * <p> An invocation of this method upon a charset <tt>cs</tt> returns the

     * same result as the expression

     *

     * <pre>

     *     cs.newDecoder()

     *       .onMalformedInput(CodingErrorAction.REPLACE)

     *       .onUnmappableCharacter(CodingErrorAction.REPLACE)

     *       .decode(bb); </pre>

     *

     * except that it is potentially more efficient because it can cache

     * decoders between successive invocations.

     *

     * <p> This method always replaces malformed-input and unmappable-character

     * sequences with this charset's default replacement byte array.  In order

     * to detect such sequences, use the {@link

     * CharsetDecoder#decode(java.nio.ByteBuffer)} method directly.  </p>

     *

     * @param  bb  The byte buffer to be decoded

     *

     * @return  A char buffer containing the decoded characters

     */

    public final CharBuffer decode(ByteBuffer bb) {

        try {

            return ThreadLocalCoders.decoderFor(this)

                .onMalformedInput(CodingErrorAction.REPLACE)

                .onUnmappableCharacter(CodingErrorAction.REPLACE)

                .decode(bb);

        } catch (CharacterCodingException x) {

            throw new Error(x);         // Can't happen

        }

    }

    /**

     * Convenience method that encodes Unicode characters into bytes in this

     * charset.

     *

     * <p> An invocation of this method upon a charset <tt>cs</tt> returns the

     * same result as the expression

     *

     * <pre>

     *     cs.newEncoder()

     *       .onMalformedInput(CodingErrorAction.REPLACE)

     *       .onUnmappableCharacter(CodingErrorAction.REPLACE)

     *       .encode(bb); </pre>

     *

     * except that it is potentially more efficient because it can cache

     * encoders between successive invocations.

     *

     * <p> This method always replaces malformed-input and unmappable-character

     * sequences with this charset's default replacement string.  In order to

     * detect such sequences, use the {@link

     * CharsetEncoder#encode(java.nio.CharBuffer)} method directly.  </p>

     *

     * @param  cb  The char buffer to be encoded

     *

     * @return  A byte buffer containing the encoded characters

     */

    public final ByteBuffer encode(CharBuffer cb) {

        try {

            return ThreadLocalCoders.encoderFor(this)

                .onMalformedInput(CodingErrorAction.REPLACE)

                .onUnmappableCharacter(CodingErrorAction.REPLACE)

                .encode(cb);

        } catch (CharacterCodingException x) {

            throw new Error(x);         // Can't happen

        }

    }

    /**

     * Convenience method that encodes a string into bytes in this charset.

     *

     * <p> An invocation of this method upon a charset <tt>cs</tt> returns the

     * same result as the expression

     *

     * <pre>

     *     cs.encode(CharBuffer.wrap(s)); </pre>

     *

     * @param  str  The string to be encoded

     *

     * @return  A byte buffer containing the encoded characters

     */

    public final ByteBuffer encode(String str) {

        return encode(CharBuffer.wrap(str));

    }

    /**

     * Compares this charset to another.

     *

     * <p> Charsets are ordered by their canonical names, without regard to

     * case. </p>

     *

     * @param  that

     *         The charset to which this charset is to be compared

     *

     * @return A negative integer, zero, or a positive integer as this charset

     *         is less than, equal to, or greater than the specified charset

     */

    public final int compareTo(Charset that) {

        return (name().compareToIgnoreCase(that.name()));

    }

    /**

     * Computes a hashcode for this charset. </p>

     *

     * @return  An integer hashcode

     */

    public final int hashCode() {

        return name().hashCode();

    }

    /**

     * Tells whether or not this object is equal to another.

     *

     * <p> Two charsets are equal if, and only if, they have the same canonical

     * names.  A charset is never equal to any other type of object.  </p>

     *

     * @return  <tt>true</tt> if, and only if, this charset is equal to the

     *          given object

     */

    public final boolean equals(Object ob) {

        if (!(ob instanceof Charset))

            return false;

        if (this == ob)

            return true;

        return name.equals(((Charset)ob).name());

    }

    /**

     * Returns a string describing this charset. </p>

     *

     * @return  A string describing this charset

     */

    public final String toString() {

        return name();

    }

}