A subclass of BreakIterator whose behavior is specified using a list of rules.
* *There are two kinds of rules, which are separated by semicolons: substitutions * and regular expressions.
* *A substitution rule defines a name that can be used in place of an expression. It * consists of a name, which is a string of characters contained in angle brackets, an equals * sign, and an expression. (There can be no whitespace on either side of the equals sign.) * To keep its syntactic meaning intact, the expression must be enclosed in parentheses or * square brackets. A substitution is visible after its definition, and is filled in using * simple textual substitution. Substitution definitions can contain other substitutions, as * long as those substitutions have been defined first. Substitutions are generally used to * make the regular expressions (which can get quite complex) shorted and easier to read. * They typically define either character categories or commonly-used subexpressions.
* *There is one special substitution. If the description defines a substitution * called "<ignore>", the expression must be a [] expression, and the * expression defines a set of characters (the "ignore characters") that * will be transparent to the BreakIterator. A sequence of characters will break the * same way it would if any ignore characters it contains are taken out. Break * positions never occur befoer ignore characters.
* *A regular expression uses a subset of the normal Unix regular-expression syntax, and * defines a sequence of characters to be kept together. With one significant exception, the * iterator uses a longest-possible-match algorithm when matching text to regular * expressions. The iterator also treats descriptions containing multiple regular expressions * as if they were ORed together (i.e., as if they were separated by |).
* *The special characters recognized by the regular-expression parser are as follows:
* *** **
** ** *Specifies that the expression preceding the asterisk may occur any number * of times (including not at all). ** *{} *Encloses a sequence of characters that is optional. ** *() *Encloses a sequence of characters. If followed by *, the sequence * repeats. Otherwise, the parentheses are just a grouping device and a way to delimit * the ends of expressions containing |. ** *| *Separates two alternative sequences of characters. Either one * sequence or the other, but not both, matches this expression. The | character can * only occur inside (). ** *. *Matches any character. ** **? *Specifies a non-greedy asterisk. *? works the same way as *, except * when there is overlap between the last group of characters in the expression preceding the * * and the first group of characters following the *. When there is this kind of * overlap, * will match the longest sequence of characters that match the expression before * the *, and *? will match the shortest sequence of characters matching the expression * before the *?. For example, if you have "xxyxyyyxyxyxxyxyxyy" in the text, * "x[xy]*x" will match through to the last x (i.e., "xxyxyyyxyxyxxyxyxyy", * but "x[xy]*?x" will only match the first two xes ("xxyxyyyxyxyxxyxyxyy"). ** *[] *Specifies a group of alternative characters. A [] expression will * match any single character that is specified in the [] expression. For more on the * syntax of [] expressions, see below. ** */ *Specifies where the break position should go if text matches this * expression. (e.g., "[a-z]*/[:Zs:]*1" will match if the iterator sees a run * of letters, followed by a run of whitespace, followed by a digit, but the break position * will actually go before the whitespace). Expressions that don't contain / put the * break position at the end of the matching text. ** *\ *Escape character. The \ itself is ignored, but causes the next * character to be treated as literal character. This has no effect for many * characters, but for the characters listed above, this deprives them of their special * meaning. (There are no special escape sequences for Unicode characters, or tabs and * newlines; these are all handled by a higher-level protocol. In a Java string, * "\n" will be converted to a literal newline character by the time the * regular-expression parser sees it. Of course, this means that \ sequences that are * visible to the regexp parser must be written as \\ when inside a Java string.) All * characters in the ASCII range except for letters, digits, and control characters are * reserved characters to the parser and must be preceded by \ even if they currently don't * mean anything. ** *! *If ! appears at the beginning of a regular expression, it tells the regexp * parser that this expression specifies the backwards-iteration behavior of the iterator, * and not its normal iteration behavior. This is generally only used in situations * where the automatically-generated backwards-iteration brhavior doesn't produce * satisfactory results and must be supplemented with extra client-specified rules. ** *(all others) *All other characters are treated as literal characters, which must match * the corresponding character(s) in the text exactly. *
Within a [] expression, a number of other special characters can be used to specify * groups of characters:
* *** **
** *- *Specifies a range of matching characters. For example * "[a-p]" matches all lowercase Latin letters from a to p (inclusive). The - * sign specifies ranges of continuous Unicode numeric values, not ranges of characters in a * language's alphabetical order: "[a-z]" doesn't include capital letters, nor does * it include accented letters such as a-umlaut. ** *:: *A pair of colons containing a one- or two-letter code matches all * characters in the corresponding Unicode category. The two-letter codes are the same * as the two-letter codes in the Unicode database (for example, "[:Sc::Sm:]" * matches all currency symbols and all math symbols). Specifying a one-letter code is * the same as specifying all two-letter codes that begin with that letter (for example, * "[:L:]" matches all letters, and is equivalent to * "[:Lu::Ll::Lo::Lm::Lt:]"). Anything other than a valid two-letter Unicode * category code or a single letter that begins a Unicode category code is illegal within * colons. ** *[] *[] expressions can nest. This has no effect, except when used in * conjunction with the ^ token. ** *^ *Excludes the character (or the characters in the [] expression) following * it from the group of characters. For example, "[a-z^p]" matches all Latin * lowercase letters except p. "[:L:^[\u4e00-\u9fff]]" matches all letters * except the Han ideographs. ** *(all others) *All other characters are treated as literal characters. (For * example, "[aeiou]" specifies just the letters a, e, i, o, and u.) *
For a more complete explanation, see http://www.ibm.com/java/education/boundaries/boundaries.html. * For examples, see the resource data (which is annotated).
* * @author Richard Gillam */ class RuleBasedBreakIterator { protected: /** * A token used as a character-category value to identify ignore characters */ static int8_t IGNORE; private: /** * The state number of the starting state */ static int16_t START_STATE; /** * The state-transition value indicating "stop" */ static int16_t STOP_STATE; /** * The textual description this iterator was created from */ UnicodeString description; /** * A table that indexes from character values to character category numbers */ CompactByteArray charCategoryTable; /** * The table of state transitions used for forward iteration */ int16_t* stateTable; /** * The table of state transitions used to sync up the iterator with the * text in backwards and random-access iteration */ int16_t* backwardsStateTable; /** * A list of flags indicating which states in the state table are accepting * ("end") states */ bool_t* endStates; /** * The number of character categories (and, thus, the number of columns in * the state tables) */ int32_t numCategories; /** * The character iterator through which this BreakIterator accesses the text */ CharacterIterator text; //======================================================================= // constructors //======================================================================= public: /** * Constructs a RuleBasedBreakIterator according to the description * provided. If the description is malformed, throws an * IllegalArgumentException. Normally, instead of constructing a * RuleBasedBreakIterator directory, you'll use the factory methods * on BreakIterator to create one indirectly from a description * in the framework's resource files. You'd use this when you want * special behavior not provided by the built-in iterators. */ RuleBasedBreakIterator(UnicodeString description); //======================================================================= // boilerplate //======================================================================= public: /** * Clones this iterator. * @return A newly-constructed RuleBasedBreakIterator with the same * behavior as this one. */ virtual Object clone(); /** * Returns true if both BreakIterators are of the same class, have the same * rules, and iterate over the same text. */ virtual bool_t equals(Object that); /** * Returns the description used to create this iterator */ virtual UnicodeString toString(); /** * Compute a hashcode for this BreakIterator * @return A hash code */ virtual int32_t hashCode(); //======================================================================= // BreakIterator overrides //======================================================================= /** * Sets the current iteration position to the beginning of the text. * (i.e., the CharacterIterator's starting offset). * @return The offset of the beginning of the text. */ virtual int32_t first(); /** * Sets the current iteration position to the end of the text. * (i.e., the CharacterIterator's ending offset). * @return The text's past-the-end offset. */ virtual int32_t last(); /** * Advances the iterator either forward or backward the specified number of steps. * Negative values move backward, and positive values move forward. This is * equivalent to repeatedly calling next() or previous(). * @param n The number of steps to move. The sign indicates the direction * (negative is backwards, and positive is forwards). * @return The character offset of the boundary position n boundaries away from * the current one. */ virtual int32_t next(int32_t n); /** * Advances the iterator to the next boundary position. * @return The position of the first boundary after this one. */ virtual int32_t next(); /** * Advances the iterator backwards, to the last boundary preceding this one. * @return The position of the last boundary position preceding this one. */ virtual int32_t previous(); /** * Sets the iterator to refer to the first boundary position following * the specified position. * @offset The position from which to begin searching for a break position. * @return The position of the first break after the current position. */ virtual int32_t following(int32_t offset); /** * Sets the iterator to refer to the last boundary position before the * specified position. * @offset The position to begin searching for a break from. * @return The position of the last boundary before the starting position. */ virtual int32_t preceding(int32_t offset); /** * Returns true if the specfied position is a boundary position. As a side * effect, leaves the iterator pointing to the first boundary position at * or after "offset". * @param offset the offset to check. * @return True if "offset" is a boundary position. */ virtual bool_t isBoundary(int32_t offset); /** * Returns the current iteration position. * @return The current iteration position. */ virtual int32_t current(); /** * Return a CharacterIterator over the text being analyzed. This version * of this method returns the actual CharacterIterator we're using internally. * Changing the state of this iterator can have undefined consequences. If * you need to change it, clone it first. * @return An iterator over the text being analyzed. */ virtual CharacterIterator getText(); /** * Set the iterator to analyze a new piece of text. This function resets * the current iteration position to the beginning of the text. * @param newText An iterator over the text to analyze. */ virtual void setText(CharacterIterator newText); //======================================================================= // implementation //======================================================================= protected: /** * This method is the actual implementation of the next() method. All iteration * vectors through here. This method initializes the state machine to state 1 * and advances through the text character by character until we reach the end * of the text or the state machine transitions to state 0. We update our return * value every time the state machine passes through a possible end state. */ virtual int32_t handleNext(); /** * This method backs the iterator back up to a "safe position" in the text. * This is a position that we know, without any context, must be a break position. * The various calling methods then iterate forward from this safe position to * the appropriate position to return. (For more information, see the description * of buildBackwardsStateTable() in RuleBasedBreakIterator.Builder.) */ virtual int32_t handlePrevious(); /** * Looks up a character's category (i.e., its category for breaking purposes, * not its Unicode category) */ virtual int32_t lookupCategory(UChar c); /** * Given a current state and a character category, looks up the * next state to transition to in the state table. */ virtual int32_t lookupState(int32_t state, int32_t category); /** * Given a current state and a character category, looks up the * next state to transition to in the backwards state table. */ virtual int32_t lookupBackwardState(int32_t state, int32_t category); }; #endif