Summary

Add UTF-32 based Charset constants into java.nio.charset.StandardCharsets class

Problem

There are Charset constants for UTF encoding schemes defined by ISO10646/Unicode in StandardCharsets. However, UTF-32 based charsets are not defined, while others (UTF-8, UTF-16 based) are defined. It would be consistent to add UTF-32 based charsets as well.

Solution

Add UTF-32BE, UTF-32LE, and UTF-32 public fields in StandardCharsets class. Also, remove "Amendment 1/2" from the existing UTF-8/16 explanations in the java.nio.charset.Charset class description, as there seems the description for UTF-8/16 are now in the main document (https://www.iso.org/obp/ui/en/#iso:std:iso-iec:10646:ed-6:v1:en).

Specification

Add the following public fields in java.nio.charset.StandardCharset class:

/**
 * Thirty-two-bit UCS Transformation Format, big-endian byte order.
 * @since 22
 */
public static final Charset UTF_32BE;

/**
 * Thirty-two-bit UCS Transformation Format, little-endian byte order.
 * @since 22
 */
public static final Charset UTF_32LE;

/**
 * Thirty-two-bit UCS Transformation Format, byte order identified by an
 * optional byte-order mark.
 * @since 22
 */
public static final Charset UTF_32;

Modify the Standard charsets section of the class description for java.nio.charset.Charset class as follows:

   *     <td>Sixteen-bit UCS Transformation Format,
   *         little-endian byte&nbsp;order</td></tr>
   * <tr><th scope="row" style="vertical-align:top">{@code UTF-16}</th>
   *     <td>Sixteen-bit UCS Transformation Format,
   *         byte&nbsp;order identified by an optional byte-order mark</td></tr>
+  * <tr><th scope="row" style="vertical-align:top">{@code UTF-32BE}</th>
+  *     <td>Thirty-two-bit UCS Transformation Format,
+  *         big-endian byte&nbsp;order</td></tr>
+  * <tr><th scope="row" style="vertical-align:top">{@code UTF-32LE}</th>
+  *     <td>Thirty-two-bit UCS Transformation Format,
+  *         little-endian byte&nbsp;order</td></tr>
+  * <tr><th scope="row" style="vertical-align:top">{@code UTF-32}</th>
+  *     <td>Thirty-two-bit UCS Transformation Format,
+  *         byte&nbsp;order identified by an optional byte-order mark</td></tr>
   * </tbody>
   * </table></blockquote>
   *
   * <p> The {@code UTF-8} 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
+  * ISO&nbsp;10646-1 and is also described in the <a
   * href="http://www.unicode.org/standard/standard.html"><i>Unicode
   * Standard</i></a>.
   *
   * <p> The {@code UTF-16} 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
+  * ISO&nbsp;10646-1 and are also described in the <a
+  * href="http://www.unicode.org/standard/standard.html"><i>Unicode
+  * Standard</i></a>.
+  *
+  * <p> The {@code UTF-32} charsets are based upon transformation formats
+  * which are specified in
+  * ISO&nbsp;10646-1 and are also described in the <a
   * href="http://www.unicode.org/standard/standard.html"><i>Unicode
   * Standard</i></a>.
   *
-  * <p> The {@code UTF-16} charsets use sixteen-bit quantities and are
+  * <p> The {@code UTF-16} and {@code UTF-32} charsets use sixteen-bit and thirty-two-bit
+  * quantities respectively, 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 <code>'&#92;uFEFF'</code>.  Byte-order marks are handled
+  * the Unicode character {@code U+FEFF}.  Byte-order marks are handled
   * as follows:
   *
   * <ul>
   *
-  *   <li><p> When decoding, the {@code UTF-16BE} and {@code UTF-16LE}
+  *   <li><p> When decoding, the {@code UTF-16BE}, {@code UTF-16LE},
+  *   {@code UTF-32BE}, and {@code UTF-32LE}
   *   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 {@code UTF-16} charset interprets the
+  *   <li><p> When decoding, the {@code UTF-16} and {@code UTF-32} charsets interpret 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>