com.ibm.icu.text

Class RuleBasedBreakIterator_Old

public class RuleBasedBreakIterator_Old extends RuleBasedBreakIterator

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, 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 (when a substitution is used, its name is enclosed in curly braces. The curly braces are optional in the substition's definition). 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) shorter 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 before ignore characters, except when the character before the ignore characters is a line or paragraph terminator.

A regular expression uses a syntax similar to 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).
+ Specifies that the expression preceding the asterisk may occur one or more times, but must occur at least once.
? Specifies that the expression preceding the asterisk may occur once or not at all (i.e., it makes the preceding expression optional).
() Encloses a sequence of characters. If followed by * or +, the sequence repeats. If followed by ?, the sequence is optional. 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:]*[1-0]" 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 behavior 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.
^ Inverts the expression. All characters the expression includes are excluded, and vice versa. (i.e., it has the effect of saying "all Unicode characters except...") This character only has its special meaning when it's the first character in the [] expression. (Generally, you only see the ^ character inside a nested [] expression used in conjunction with the syntax below.)
(all others) All other characters are treated as literal characters.  (For example, "[aeiou]" specifies just the letters a, e, i, o, and u.)

[] expressions can nest. There are some other characters that have special meaning only when used in conjunction with nester [] expressions:

For a more complete explanation, see http://icu.sourceforge.net/docs/papers/text_boundary_analysis_in_java/.   For examples, see the resource data (which is annotated).

Author: Richard Gillam

UNKNOWN: ICU 2.0

:: Within a nested [] expression, a pair of colons containing a one- or two-letter code matches all characters in the corresponding Unicode category.  The :: expression has to be the only thing inside the [] expression. 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 valide Unicode category code is illegal within the colons.
| Two nested [] expressions juxtaposed or separated only by a | character are merged together into a single [] expression matching all the characters in either of the original [] expressions. (e.g., "[[ab][bc]]" is equivalent to "[abc]", and so is "[[ab]|[bc]]". NOTE: "[ab][bc]" is NOT the same thing as "[[ab][bc]]". The first expression will match two characters: an a or b followed by either another b or a c. The second expression will match a single character, which may be a, b, or c. The nesting is required for the expressions to merge together.
& Two nested [] expressions with only & between them will match any character that appears in both nested [] expressions (this is a set intersection). (e.g., "[[ab]&[bc]]" will only match the letter b.)
- Two nested [] expressions with - between them will match any character that appears in the first nested [] expression but not the second one (this is an asymmetrical set difference). (e.g., "[[:Sc:]-[$]]" matches any currency symbol except the dollar sign. "[[ab]-[bc]] will match only the letter a. This has exactly the same effect as "[[ab]&[^bc]]".)
Nested Class Summary
protected classRuleBasedBreakIterator_Old.Builder
The Builder class has the job of constructing a RuleBasedBreakIterator_Old from a textual description.
Field Summary
protected static byteIGNORE
A token used as a character-category value to identify ignore characters
Constructor Summary
RuleBasedBreakIterator_Old(String description)
Constructs a RuleBasedBreakIterator_Old according to the description provided.
Method Summary
protected static voidcheckOffset(int offset, CharacterIterator text)
Throw IllegalArgumentException unless begin <= offset < end.
Objectclone()
Clones this iterator.
intcurrent()
Returns the current iteration position.
voiddebugDumpTables()
Dump out a more-or-less human readable form of the complete state table and character class definitions
static voiddebugPrintln(String s)
booleanequals(Object that)
Returns true if both BreakIterators are of the same class, have the same rules, and iterate over the same text.
intfirst()
Sets the current iteration position to the beginning of the text. (i.e., the CharacterIterator's starting offset).
intfollowing(int offset)
Sets the iterator to refer to the first boundary position following the specified position.
intgetRuleStatus()
Return the status tag from the break rule that determined the most recently returned break position.
intgetRuleStatusVec(int[] fillInArray)
Get the status (tag) values from the break rule(s) that determined the most recently returned break position.
CharacterIteratorgetText()
Return a CharacterIterator over the text being analyzed.
protected inthandleNext()
This method is the actual implementation of the next() method.
protected inthandlePrevious()
This method backs the iterator back up to a "safe position" in the text.
inthashCode()
Compute a hashcode for this BreakIterator
booleanisBoundary(int offset)
Returns true if the specfied position is a boundary position.
intlast()
Sets the current iteration position to the end of the text. (i.e., the CharacterIterator's ending offset).
protected intlookupBackwardState(int state, int category)
Given a current state and a character category, looks up the next state to transition to in the backwards state table.
protected intlookupCategory(char c)
Looks up a character's category (i.e., its category for breaking purposes, not its Unicode category)
protected intlookupState(int state, int category)
Given a current state and a character category, looks up the next state to transition to in the state table.
protected RuleBasedBreakIterator_Old.BuildermakeBuilder()
Creates a Builder.
intnext(int n)
Advances the iterator either forward or backward the specified number of steps.
intnext()
Advances the iterator to the next boundary position.
intpreceding(int offset)
Sets the iterator to refer to the last boundary position before the specified position.
intprevious()
Advances the iterator backwards, to the last boundary preceding this one.
voidsetText(CharacterIterator newText)
Set the iterator to analyze a new piece of text.
StringtoString()
Returns the description used to create this iterator
protected voidwriteSwappedInt(int x, DataOutputStream out, boolean littleEndian)
protected voidwriteSwappedShort(short x, DataOutputStream out, boolean littleEndian)
voidwriteTablesToFile(FileOutputStream file, boolean littleEndian)
Write the RBBI runtime engine state transition tables to a file.

Field Detail

IGNORE

protected static final byte IGNORE
A token used as a character-category value to identify ignore characters

UNKNOWN: ICU 2.0

Constructor Detail

RuleBasedBreakIterator_Old

public RuleBasedBreakIterator_Old(String description)
Constructs a RuleBasedBreakIterator_Old according to the description provided. If the description is malformed, throws an IllegalArgumentException. Normally, instead of constructing a RuleBasedBreakIterator_Old 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.

UNKNOWN: ICU 2.0

Method Detail

checkOffset

protected static final void checkOffset(int offset, CharacterIterator text)
Throw IllegalArgumentException unless begin <= offset < end.

UNKNOWN: ICU 2.0

clone

public Object clone()
Clones this iterator.

Returns: A newly-constructed RuleBasedBreakIterator_Old with the same behavior as this one.

UNKNOWN: ICU 2.0

current

public int current()
Returns the current iteration position.

Returns: The current iteration position.

UNKNOWN: ICU 2.0

debugDumpTables

public void debugDumpTables()
Dump out a more-or-less human readable form of the complete state table and character class definitions

UNKNOWN:

debugPrintln

public static void debugPrintln(String s)

UNKNOWN:

equals

public boolean equals(Object that)
Returns true if both BreakIterators are of the same class, have the same rules, and iterate over the same text.

UNKNOWN: ICU 2.0

first

public int first()
Sets the current iteration position to the beginning of the text. (i.e., the CharacterIterator's starting offset).

Returns: The offset of the beginning of the text.

UNKNOWN: ICU 2.0

following

public int following(int offset)
Sets the iterator to refer to the first boundary position following the specified position.

Parameters: offset The position from which to begin searching for a break position.

Returns: The position of the first break after the current position.

UNKNOWN: ICU 2.0

getRuleStatus

public int getRuleStatus()
Return the status tag from the break rule that determined the most recently returned break position. The values appear in the rule source within brackets, {123}, for example. For rules that do not specify a status, a default value of 0 is returned. If more than one rule applies, the numerically largest of the possible status values is returned.

Note that for old style break iterators (implemented by this class), no status can be declared, and a status of zero is always assumed.

UNKNOWN: ICU 3.0 This API might change or be removed in a future release.

getRuleStatusVec

public int getRuleStatusVec(int[] fillInArray)
Get the status (tag) values from the break rule(s) that determined the most recently returned break position. The values appear in the rule source within brackets, {123}, for example. The default status value for rules that do not explicitly provide one is zero.

Note that for old style break iterators (implemented by this class), no status can be declared, and a status of zero is always assumed.

UNKNOWN: ICU 3.0 This API might change or be removed in a future release.

getText

public CharacterIterator getText()
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.

Returns: An iterator over the text being analyzed.

UNKNOWN: ICU 2.0

handleNext

protected int handleNext()
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.

UNKNOWN: ICU 2.0

handlePrevious

protected int handlePrevious()
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_Old.Builder.)

UNKNOWN: ICU 2.0

hashCode

public int hashCode()
Compute a hashcode for this BreakIterator

Returns: A hash code

UNKNOWN: ICU 2.0

isBoundary

public boolean isBoundary(int 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".

Parameters: offset the offset to check.

Returns: True if "offset" is a boundary position.

UNKNOWN: ICU 2.0

last

public int last()
Sets the current iteration position to the end of the text. (i.e., the CharacterIterator's ending offset).

Returns: The text's past-the-end offset.

UNKNOWN: ICU 2.0

lookupBackwardState

protected int lookupBackwardState(int state, int category)
Given a current state and a character category, looks up the next state to transition to in the backwards state table.

UNKNOWN:

lookupCategory

protected int lookupCategory(char c)
Looks up a character's category (i.e., its category for breaking purposes, not its Unicode category)

UNKNOWN:

lookupState

protected int lookupState(int state, int category)
Given a current state and a character category, looks up the next state to transition to in the state table.

UNKNOWN:

makeBuilder

protected RuleBasedBreakIterator_Old.Builder makeBuilder()
Creates a Builder.

UNKNOWN: ICU 2.0

next

public int next(int n)
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().

Parameters: n The number of steps to move. The sign indicates the direction (negative is backwards, and positive is forwards).

Returns: The character offset of the boundary position n boundaries away from the current one.

UNKNOWN: ICU 2.0

next

public int next()
Advances the iterator to the next boundary position.

Returns: The position of the first boundary after this one.

UNKNOWN: ICU 2.0

preceding

public int preceding(int offset)
Sets the iterator to refer to the last boundary position before the specified position.

Parameters: offset The position to begin searching for a break from.

Returns: The position of the last boundary before the starting position.

UNKNOWN: ICU 2.0

previous

public int previous()
Advances the iterator backwards, to the last boundary preceding this one.

Returns: The position of the last boundary position preceding this one.

UNKNOWN: ICU 2.0

setText

public void setText(CharacterIterator newText)
Set the iterator to analyze a new piece of text. This function resets the current iteration position to the beginning of the text.

Parameters: newText An iterator over the text to analyze.

UNKNOWN: ICU 2.0

toString

public String toString()
Returns the description used to create this iterator

UNKNOWN: ICU 2.0

writeSwappedInt

protected void writeSwappedInt(int x, DataOutputStream out, boolean littleEndian)

UNKNOWN:

writeSwappedShort

protected void writeSwappedShort(short x, DataOutputStream out, boolean littleEndian)

UNKNOWN:

writeTablesToFile

public void writeTablesToFile(FileOutputStream file, boolean littleEndian)
Write the RBBI runtime engine state transition tables to a file. Formerly used to export the tables to the C++ RBBI Implementation. Now obsolete, as C++ builds its own tables.

UNKNOWN:

Copyright (c) 2006 IBM Corporation and others.