Java in a Nutshell, 5th Edition [Electronic resources] نسخه متنی

A Charset
represents a character set or encoding.
Each Charset has a cannonical name, returned by
name( ), and a
set of aliases, returned by aliases(
). You can look up a
Charset by name or alias with the static
Charset.forName( ) method, which throws an
UnsupportedCharsetException if the named charset
is not installed on the system. In Java 5.0, you can obtain the
default Charset used by the Java VM with the
static defaultCharset(
) method. Check whether a charset specified by
name or alias is supported with the static isSupported(
). Obtain the complete set of installed
charsets with availableCharsets(
) which returns a sorted map from
canonical names to Charset objects.
Note that charset names are not
case-sensitive, and you can use any capitialization for charset names
you pass to isSupported( ) and forName(
). Note that there are a number of classes and methods in
the Java platform that specify charsets by name rather than by
Charset object. See, for example,
java.io.InputStreamReader,
java.io.OutputStreamWriter,
String.getBytes( ), and
java.nio.channels.Channels.newWriter( ). When
working with classes and methods such as these, there is no need to
use a Charset object.

All implementations of Java are required to support at least the
following 6 charsets:

Once you have obtained a Charset with
forName( ) or availableCharsets(
), you can use the encode(
) method to
encode a String or CharBuffer
of text into a ByteBuffer, or you can use the
decode( ) method to convert the bytes in a
ByteBuffer into characters in a
CharBuffer. These convenience methods create a new
CharsetEncoder or
CharsetDecoder, specify that malformed input or
unmappable characters or bytes should be replaced with the default
replacement string or bytes, and then invoke the encode(
) or decode( ) method of the encoder or
decoder. For full control over the encoding and decoding process, you
may prefer to obtain your own CharsetEncoder or
CharsetDecoder object with newEncoder(
)
or newDecoder(
). See CharsetDecoder for details.

Instead of using a Charset,
CharsetEncoder, or
CharsetDecoder directly, you may also pass an
encoder or decoder to the static methods of
java.nio.channels.Channels to obtain a
java.io.Reader
or
java.io.Writer that you can use to read or write
characters from or to a byte-oriented Channel.

Note that not all Charset objects support encoding
("auto-detect" charsets can
determine the source charset when decoding, but have no way to
encode). Use canEncode( ) to determine whether a
given Charset can encode.

Charset also defines, implements, or overrides
various other methods. displayName( ) returns a
localized name for the charset, or returns the cannonical name if
there is no localization. toString( ) returns an
implementation-dependent textual representation of the charset. The
equals( ) method
compares two charsets by comparing their canonical names.
Charset implements Comparable,
and its compareTo( ) method
orders charsets by their canonical name. contains(
) returns true if a specified charset is
"contained in" this charset. That
is, if every character that can be represented in the specified
charset can also be represented in this charset. Note that those
representations need not be the same, however. isRegistered(
) returns
true if the charset is registered with the
IANA
charset registry (see http://www.iana.org/assignments/character-sets.)

Figure 13-48. java.nio.charset.Charset

public abstract class

Charset implements Comparable<Charset> {
// Protected Constructors
protected

Charset (String

canonicalName , String[ ]

aliases );
// Public Class Methods
public static java.util.SortedMap<String,Charset>

availableCharsets ( );

5.0 public static Charset

defaultCharset ( );
public static Charset

forName (String

charsetName );
public static boolean

isSupported (String

charsetName );
// Public Instance Methods
public final java.util.Set<String>

aliases ( );
public boolean

canEncode ( ); constant
public abstract boolean

contains (Charset

cs );
public final java.nio.CharBuffer

decode (java.nio.ByteBuffer

bb );
public String

displayName ( );
public String

displayName (java.util.Locale

locale );
public final java.nio.ByteBuffer

encode (java.nio.CharBuffer

cb );
public final java.nio.ByteBuffer

encode (String

str );
public final boolean

isRegistered ( );
public final String

name ( );
public abstract CharsetDecoder

newDecoder ( );
public abstract CharsetEncoder

newEncoder ( );
// Methods Implementing Comparable

5.0 public final int

compareTo (Charset

that );
// Public Methods Overriding Object
public final boolean

equals (Object

ob );
public final int

hashCode ( );
public final String

toString ( );
}