重新学习Java语言（一）--Java语言的标识符和关键字

/**
     * Determines if the character (Unicode code point) may be part of a Java
     * identifier as other than the first character.
     * <p>
     * A character may be part of a Java identifier if any of the following
     * are true:
     * <ul>
     * <li>  it is a letter                                                        字母组合（单词）
     * <li>  it is a currency symbol (such as {@code '$'})                         货币符号如：美元符号
     * <li>  it is a connecting punctuation character (such as {@code '_'})        连接标点字符如：下划线
     * <li>  it is a digit                                                         数字
     * <li>  it is a numeric letter (such as a Roman numeral character)            数字字母如：罗马数字等
     * <li>  it is a combining mark                                                结合字符（举例说明）
     * <li>  it is a non-spacing mark                                              非空格标记（举例说明）
     * <li> {@link #isIdentifierIgnorable(int)
     * isIdentifierIgnorable(codePoint)} returns {@code true} for
     * the character
     * </ul>
     *
     * @param   codePoint the character (Unicode code point) to be tested.
     * @return {@code true} if the character may be part of a
     *          Java identifier; {@code false} otherwise.
     * @see     Character#isIdentifierIgnorable(int)
     * @see     Character#isJavaIdentifierStart(int)
     * @see     Character#isLetterOrDigit(int)
     * @see     Character#isUnicodeIdentifierPart(int)
     * @see     javax.lang.model.SourceVersion#isIdentifier(CharSequence)
     * @since   1.5
     */
    public static boolean isJavaIdentifierPart(int codePoint) {
        return CharacterData.of(codePoint).isJavaIdentifierPart(codePoint);
    }

package java.lang;

abstract class CharacterData {
    abstract int getProperties(int ch);
    abstract int getType(int ch);
    abstract boolean isWhitespace(int ch);
    abstract boolean isMirrored(int ch);
    abstract boolean isJavaIdentifierStart(int ch);
    abstract boolean isJavaIdentifierPart(int ch);
    abstract boolean isUnicodeIdentifierStart(int ch);
    abstract boolean isUnicodeIdentifierPart(int ch);
    abstract boolean isIdentifierIgnorable(int ch);
    abstract int toLowerCase(int ch);
    abstract int toUpperCase(int ch);
    abstract int toTitleCase(int ch);
    abstract int digit(int ch, int radix);
    abstract int getNumericValue(int ch);
    abstract byte getDirectionality(int ch);

    //need to implement for JSR204
    int toUpperCaseEx(int ch) {
        return toUpperCase(ch);
    }

    char[] toUpperCaseCharArray(int ch) {
        return null;
    }

    boolean isOtherLowercase(int ch) {
        return false;
    }

    boolean isOtherUppercase(int ch) {
        return false;
    }

    boolean isOtherAlphabetic(int ch) {
        return false;
    }

    boolean isIdeographic(int ch) {
        return false;
    }

    // Character <= 0xff (basic latin) is handled by internal fast-path
    // to avoid initializing large tables.
    // Note: performance of this "fast-path" code may be sub-optimal
    // in negative cases for some accessors due to complicated ranges.
    // Should revisit after optimization of table initialization.

    static final CharacterData of(int ch) {
        if (ch >>> 8 == 0) {     // fast-path
            return CharacterDataLatin1.instance;
        } else {
            switch(ch >>> 16) {  //plane 00-16
            case(0):
                return CharacterData00.instance;
            case(1):
                return CharacterData01.instance;
            case(2):
                return CharacterData02.instance;
            case(14):
                return CharacterData0E.instance;
            case(15):   // Private Use
            case(16):   // Private Use
                return CharacterDataPrivateUse.instance;
            default:
                return CharacterDataUndefined.instance;
            }
        }
    }
}              //假设传参获得的实例是

boolean isJavaIdentifierPart(int ch) {
        int props = getProperties(ch);
        return ((props & 0x00003000) != 0);
    }


    int getProperties(int ch) {
        char offset = (char)ch;
        int props = A[Y[X[offset>>5]|((offset>>1)&0xF)]|(offset&0x1)];
        return props;
    }