/*
 * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
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 *
 *
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 *
 *
 *
 *
 *
 *
 *
 */

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.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><a name="charenc"></a>
 * <h2>Charset names</h2>
 *
 * <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.
 *
 * <p><a name="hn">Some charsets have an <i>historical name</i> that is defined for
 * compatibility with previous versions of the Java platform.</a> 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.
 *
 * <p><a name="iana"> </a>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.
 *
 *
 * <h2>Standard charsets</h2>
 *
 *
 *
 * <p><a name="standard">Every implementation of the Java platform is required to support the
 * following standard charsets.</a> 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 align="left">Charset</th><th align="left">Description</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 occurring 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.
 *
 * <h2>Terminology</h2>
 *
 * <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&nbsp;8859-1,
 * JIS&nbsp;X&nbsp;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&nbsp;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&nbsp;X&nbsp;0201, JIS&nbsp;X&nbsp;0208, and JIS&nbsp;X&nbsp;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<CharsetProvider> providers() {
 return new Iterator<CharsetProvider>() {

 ClassLoader cl = ClassLoader.getSystemClassLoader();
 ServiceLoader<CharsetProvider> sl =
 ServiceLoader.load(CharsetProvider.class, cl);
 Iterator<CharsetProvider> i = sl.iterator();

 CharsetProvider 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 CharsetProvider next() {
 if (!getNext())
 throw new NoSuchElementException();
 CharsetProvider 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<CharsetProvider> i = providers();
 i.hasNext();) {
 CharsetProvider cp = 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 class ExtendedProviderHolder {
 static final CharsetProvider extendedProvider = extendedProvider();
 // returns ExtendedProvider, if installed
 private static CharsetProvider extendedProvider() {
 return AccessController.doPrivileged(
 new PrivilegedAction<CharsetProvider>() {
 public CharsetProvider run() {
 try {
 Class<?> epc
 = Class.forName("sun.nio.cs.ext.ExtendedCharsets");
 return (CharsetProvider)epc.newInstance();
 } catch (ClassNotFoundException x) {
 // Extended charsets not available
 // (charsets.jar not present)
 } catch (InstantiationException |
 IllegalAccessException x) {
 throw new Error(x);
 }
 return null;
 }
 });
 }
 }

 private static Charset lookupExtendedCharset(String charsetName) {
 CharsetProvider ecp = ExtendedProviderHolder.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.
 *
 * @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.
 *
 * @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);
 CharsetProvider ecp = ExtendedProviderHolder.extendedProvider;
 if (ecp != null)
 put(ecp.charsets(), m);
 for (Iterator<CharsetProvider> i = providers(); i.hasNext();) {
 CharsetProvider cp = 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.
 *
 * @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.
 *
 * @return The canonical name of this charset
 */
 public final String name() {
 return name;
 }

 /**
 * Returns a set containing this charset's aliases.
 *
 * @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>.
 *
 * @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.
 *
 * @param cs
 * The given 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.
 *
 * @return A new decoder for this charset
 */
 public abstract CharsetDecoder newDecoder();

 /**
 * Constructs a new encoder for this charset.
 *
 * @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.
 *
 * @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.
 *
 * @return A string describing this charset
 */
 public final String toString() {
 return name();
 }

}