/*

  * 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();

     }

 }