Charset for encoding and decoding bytes as hexidecimal

HexCharset.java

public class HexCharset extends Charset {

        public static final HexCharset INSTANCE = new HexCharset();

        private HexCharset() {
            super("hex", new String[0]);
        }

        @Override
        public boolean contains(Charset cs) {
            return cs instanceof HexCharset;
        }

        @Override
        public CharsetDecoder newDecoder() {
            return new CharsetDecoder(HexCharset.this, 2f, 2f) {
                @Override
                protected CoderResult decodeLoop(ByteBuffer in, CharBuffer out) {
                    while (in.hasRemaining()) {
                        if (out.remaining() < 1) {
                            return CoderResult.OVERFLOW;
                        }
                        byte b = in.get();
                        out.append(HEX_DIGITS[(b >> 4) & 0xf]);
                        out.append(HEX_DIGITS[b & 0xf]);
                    }
                    return CoderResult.UNDERFLOW;
                }
            };
        }

        @Override
        public CharsetEncoder newEncoder() {
            return new CharsetEncoder(this, 0.5f, 1) {
                @Override
                protected CoderResult encodeLoop(CharBuffer in, ByteBuffer out) {
                    if (in.remaining() % 2 != 0) {
                        throw new IllegalArgumentException("Unexpected number of characters: " + in.remaining());
                    }
                    while (in.hasRemaining()) {
                        if (!out.hasRemaining()) {
                            return CoderResult.OVERFLOW;
                        }

                        char c1 = in.get();
                        char c2 = in.get();
                        int d1 = decodeHexDigit(c1);
                        int d2 = decodeHexDigit(c2);
                        out.put((byte) ((d1 << 4) + d2));
                    }
                    return CoderResult.UNDERFLOW;
                }
            };
        }

        // @formatter:off
        private static final char[] HEX_DIGITS = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
        private static int decodeHexDigit(char c) {
            if (c >= '0' && c <= '9') { return c - '0'; }
            if (c >= 'a' && c <= 'f') { return c - 'a' + 10; }
            if (c >= 'A' && c <= 'F') { return c - 'A' + 10; }
            throw new IllegalArgumentException("Unexpected hex digit: " + c);
        }
        // @formatter:on
    }