/*
 
* Copyright (c) 2000, 2013, 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.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
 
*
 
*
 
*/


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
  
bbThe 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
  
cbThe 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
  
strThe 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();
    
}

}