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DictionaryBasedBreakIterator Class Reference

A subclass of RuleBasedBreakIterator that adds the ability to use a dictionary to further subdivide ranges of text beyond what is possible using just the state-table-based algorithm. More...

#include <dbbi.h>

Inheritance diagram for DictionaryBasedBreakIterator:

RuleBasedBreakIterator BreakIterator

Public Member Functions

virtual ~DictionaryBasedBreakIterator ()
 Destructor.
DictionaryBasedBreakIteratoroperator= (const DictionaryBasedBreakIterator &that)
 Assignment operator.
virtual BreakIteratorclone (void) const
 Returns a newly-constructed RuleBasedBreakIterator with the same behavior, and iterating over the same text, as this one.
virtual int32_t previous (void)
 Advances the iterator backwards, to the last boundary preceding this one.
virtual int32_t following (int32_t offset)
 Sets the iterator to refer to the first boundary position following the specified position.
virtual int32_t preceding (int32_t offset)
 Sets the iterator to refer to the last boundary position before the specified position.
virtual UClassID getDynamicClassID (void) const
 Returns a unique class ID POLYMORPHICALLY.

Static Public Member Functions

static UClassID getStaticClassID (void)
 Returns the class ID for this class.

Protected Member Functions

virtual int32_t handleNext (void)
 This method is the actual implementation of the next() method.
virtual void reset (void)
 dumps the cache of break positions (usually in response to a change in position of some sort)
virtual BreakIteratorcreateBufferClone (void *stackBuffer, int32_t &BufferSize, UErrorCode &status)
 Thread safe client-buffer-based cloning operation Do NOT call delete on a safeclone, since 'new' is not used to create it.

Friends

class DictionaryBasedBreakIteratorTables
class BreakIterator

Detailed Description

A subclass of RuleBasedBreakIterator that adds the ability to use a dictionary to further subdivide ranges of text beyond what is possible using just the state-table-based algorithm.

This is necessary, for example, to handle word and line breaking in Thai, which doesn't use spaces between words. The state-table-based algorithm used by RuleBasedBreakIterator is used to divide up text as far as possible, and then contiguous ranges of letters are repeatedly compared against a list of known words (i.e., the dictionary) to divide them up into words.

DictionaryBasedBreakIterator uses the same rule language as RuleBasedBreakIterator, but adds one more special substitution name: <dictionary>. This substitution name is used to identify characters in words in the dictionary. The idea is that if the iterator passes over a chunk of text that includes two or more characters in a row that are included in <dictionary>, it goes back through that range and derives additional break positions (if possible) using the dictionary.

DictionaryBasedBreakIterator is also constructed with the filename of a dictionary file. It follows a prescribed search path to locate the dictionary (right now, it looks for it in /com/ibm/text/resources in each directory in the classpath, and won't find it in JAR files, but this location is likely to change). The dictionary file is in a serialized binary format. We have a very primitive (and slow) BuildDictionaryFile utility for creating dictionary files, but aren't currently making it public. Contact us for help.

NOTE The DictionaryBasedIterator class is still under development. The APIs are not in stable condition yet.


Member Function Documentation

virtual BreakIterator* DictionaryBasedBreakIterator::createBufferClone void *  stackBuffer,
int32_t &  BufferSize,
UErrorCode status
[protected, virtual]
 

Thread safe client-buffer-based cloning operation Do NOT call delete on a safeclone, since 'new' is not used to create it.

Parameters:
stackBuffer user allocated space for the new clone. If NULL new memory will be allocated. If buffer is not large enough, new memory will be allocated.
BufferSize reference to size of allocated space. If BufferSize == 0, a sufficient size for use in cloning will be returned ('pre-flighting') If BufferSize is not enough for a stack-based safe clone, new memory will be allocated.
status to indicate whether the operation went on smoothly or there were errors An informational status value, U_SAFECLONE_ALLOCATED_ERROR, is used if any allocations were necessary.
Returns:
pointer to the new clone
ICU 1.8

Reimplemented from RuleBasedBreakIterator.

virtual int32_t DictionaryBasedBreakIterator::following int32_t  offset  )  [virtual]
 

Sets the iterator to refer to the first boundary position following the specified position.

The position from which to begin searching for a break position.

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

Reimplemented from RuleBasedBreakIterator.

UClassID DictionaryBasedBreakIterator::getDynamicClassID void   )  const [inline, virtual]
 

Returns a unique class ID POLYMORPHICALLY.

Pure virtual override. This method is to implement a simple version of RTTI, since not all C++ compilers support genuine RTTI. Polymorphic operator==() and clone() methods call this method.

Returns:
The class ID for this object. All objects of a given class have the same class ID. Objects of other classes have different class IDs.

Reimplemented from RuleBasedBreakIterator.

UClassID DictionaryBasedBreakIterator::getStaticClassID void   )  [inline, static]
 

Returns the class ID for this class.

This is useful only for comparing to a return value from getDynamicClassID(). For example:

Base* polymorphic_pointer = createPolymorphicObject(); if (polymorphic_pointer->getDynamicClassID() == Derived::getStaticClassID()) ...

Returns:
The class ID for all objects of this class.

Reimplemented from RuleBasedBreakIterator.

virtual int32_t DictionaryBasedBreakIterator::handleNext void   )  [protected, virtual]
 

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.

Reimplemented from RuleBasedBreakIterator.

DictionaryBasedBreakIterator& DictionaryBasedBreakIterator::operator= const DictionaryBasedBreakIterator that  ) 
 

Assignment operator.

Sets this iterator to have the same behavior, and iterate over the same text, as the one passed in.

virtual int32_t DictionaryBasedBreakIterator::preceding int32_t  offset  )  [virtual]
 

Sets the iterator to refer to the last boundary position before the specified position.

The position to begin searching for a break from.

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

Reimplemented from RuleBasedBreakIterator.

virtual int32_t DictionaryBasedBreakIterator::previous void   )  [virtual]
 

Advances the iterator backwards, to the last boundary preceding this one.

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

Reimplemented from RuleBasedBreakIterator.


The documentation for this class was generated from the following file:
Generated on Mon May 23 13:34:43 2005 for ICU 2.1 by  doxygen 1.4.2