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BreakIterator

public abstract class BreakIterator
extends Object implements Cloneable

java.lang.Object
   ↳ android.icu.text.BreakIterator


[icu enhancement] ICU's replacement for BreakIterator. Methods, fields, and other functionality specific to ICU are labeled '[icu]'.

A class that locates boundaries in text. This class defines a protocol for objects that break up a piece of natural-language text according to a set of criteria. Instances or subclasses of BreakIterator can be provided, for example, to break a piece of text into words, sentences, or logical characters according to the conventions of some language or group of languages. We provide five built-in types of BreakIterator:

  • getTitleInstance() returns a BreakIterator that locates boundaries between title breaks.
  • getSentenceInstance() returns a BreakIterator that locates boundaries between sentences. This is useful for triple-click selection, for example.
  • getWordInstance() returns a BreakIterator that locates boundaries between words. This is useful for double-click selection or "find whole words" searches. This type of BreakIterator makes sure there is a boundary position at the beginning and end of each legal word. (Numbers count as words, too.) Whitespace and punctuation are kept separate from real words.
  • getLineInstance() returns a BreakIterator that locates positions where it is legal for a text editor to wrap lines. This is similar to word breaking, but not the same: punctuation and whitespace are generally kept with words (you don't want a line to start with whitespace, for example), and some special characters can force a position to be considered a line-break position or prevent a position from being a line-break position.
  • getCharacterInstance() returns a BreakIterator that locates boundaries between logical characters. Because of the structure of the Unicode encoding, a logical character may be stored internally as more than one Unicode code point. (A with an umlaut may be stored as an a followed by a separate combining umlaut character, for example, but the user still thinks of it as one character.) This iterator allows various processes (especially text editors) to treat as characters the units of text that a user would think of as characters, rather than the units of text that the computer sees as "characters".
The text boundary positions are found according to the rules described in Unicode Standard Annex #29, Text Boundaries, and Unicode Standard Annex #14, Line Breaking Properties. These are available at http://www.unicode.org/reports/tr14/ and http://www.unicode.org/reports/tr29/.

BreakIterator's interface follows an "iterator" model (hence the name), meaning it has a concept of a "current position" and methods like first(), last(), next(), and previous() that update the current position. All BreakIterators uphold the following invariants:

  • The beginning and end of the text are always treated as boundary positions.
  • The current position of the iterator is always a boundary position (random- access methods move the iterator to the nearest boundary position before or after the specified position, not _to_ the specified position).
  • DONE is used as a flag to indicate when iteration has stopped. DONE is only returned when the current position is the end of the text and the user calls next(), or when the current position is the beginning of the text and the user calls previous().
  • Break positions are numbered by the positions of the characters that follow them. Thus, under normal circumstances, the position before the first character is 0, the position after the first character is 1, and the position after the last character is 1 plus the length of the string.
  • The client can change the position of an iterator, or the text it analyzes, at will, but cannot change the behavior. If the user wants different behavior, he must instantiate a new iterator.
BreakIterator accesses the text it analyzes through a CharacterIterator, which makes it possible to use BreakIterator to analyze text in any text-storage vehicle that provides a CharacterIterator interface. When BreakIterator.setText(CharacterIterator) or getText() was called, the CharacterIterator must not be modified, or else the BreakIterator behavior is undefined. In particular, call BreakIterator.setText(), not CharacterIterator.setText(). Note: Some types of BreakIterator can take a long time to create, and instances of BreakIterator are not currently cached by the system. For optimal performance, keep instances of BreakIterator around as long as makes sense. For example, when word-wrapping a document, don't create and destroy a new BreakIterator for each line. Create one break iterator for the whole document (or whatever stretch of text you're wrapping) and use it to do the whole job of wrapping the text.

Examples:

Creating and using text boundaries

 public static void main(String args[]) {
      if (args.length == 1) {
          String stringToExamine = args[0];
          //print each word in order
          BreakIterator boundary = BreakIterator.getWordInstance();
          boundary.setText(stringToExamine);
          printEachForward(boundary, stringToExamine);
          //print each sentence in reverse order
          boundary = BreakIterator.getSentenceInstance(Locale.US);
          boundary.setText(stringToExamine);
          printEachBackward(boundary, stringToExamine);
          printFirst(boundary, stringToExamine);
          printLast(boundary, stringToExamine);
      }
 }
 
Print each element in order
 public static void printEachForward(BreakIterator boundary, String source) {
     int start = boundary.first();
     for (int end = boundary.next();
          end != BreakIterator.DONE;
          start = end, end = boundary.next()) {
          System.out.println(source.substring(start,end));
     }
 }
 
Print each element in reverse order
 public static void printEachBackward(BreakIterator boundary, String source) {
     int end = boundary.last();
     for (int start = boundary.previous();
          start != BreakIterator.DONE;
          end = start, start = boundary.previous()) {
         System.out.println(source.substring(start,end));
     }
 }
 
Print first element
 public static void printFirst(BreakIterator boundary, String source) {
     int start = boundary.first();
     int end = boundary.next();
     System.out.println(source.substring(start,end));
 }
 
Print last element
 public static void printLast(BreakIterator boundary, String source) {
     int end = boundary.last();
     int start = boundary.previous();
     System.out.println(source.substring(start,end));
 }
 
Print the element at a specified position
 public static void printAt(BreakIterator boundary, int pos, String source) {
     int end = boundary.following(pos);
     int start = boundary.previous();
     System.out.println(source.substring(start,end));
 }
 
Find the next word
 public static int nextWordStartAfter(int pos, String text) {
     BreakIterator wb = BreakIterator.getWordInstance();
     wb.setText(text);
     int wordStart = wb.following(pos);
     for (;;) {
         int wordLimit = wb.next();
         if (wordLimit == BreakIterator.DONE) {
             return BreakIterator.DONE;
         }
         int wordStatus = wb.getRuleStatus();
         if (wordStatus != BreakIterator.WORD_NONE) {
             return wordStart;
         }
         wordStart = wordLimit;
      }
 }
 
The iterator returned by getWordInstance() is unique in that the break positions it returns don't represent both the start and end of the thing being iterated over. That is, a sentence-break iterator returns breaks that each represent the end of one sentence and the beginning of the next. With the word-break iterator, the characters between two boundaries might be a word, or they might be the punctuation or whitespace between two words. The above code uses getRuleStatus() to identify and ignore boundaries associated with punctuation or other non-word characters.

See also:

Summary

Constants

int DONE

DONE is returned by previous() and next() after all valid boundaries have been returned.

int KIND_CHARACTER

[icu]

int KIND_LINE

[icu]

int KIND_SENTENCE

[icu]

int KIND_TITLE

[icu]

int KIND_WORD

[icu]

int WORD_IDEO

Tag value for words containing ideographic characters, lower limit

int WORD_IDEO_LIMIT

Tag value for words containing ideographic characters, upper limit

int WORD_KANA

Tag value for words containing kana characters, lower limit

int WORD_KANA_LIMIT

Tag value for words containing kana characters, upper limit

int WORD_LETTER

Tag value for words that contain letters, excluding hiragana, katakana or ideographic characters, lower limit.

int WORD_LETTER_LIMIT

Tag value for words containing letters, upper limit

int WORD_NONE

Tag value for "words" that do not fit into any of other categories.

int WORD_NONE_LIMIT

Upper bound for tags for uncategorized words.

int WORD_NUMBER

Tag value for words that appear to be numbers, lower limit.

int WORD_NUMBER_LIMIT

Tag value for words that appear to be numbers, upper limit.

Protected constructors

BreakIterator()

Default constructor.

Public methods

Object clone()

Clone method.

abstract int current()

Return the iterator's current position.

abstract int first()

Set the iterator to the first boundary position.

abstract int following(int offset)

Sets the iterator's current iteration position to be the first boundary position following the specified position.

static Locale[] getAvailableLocales()

Returns a list of locales for which BreakIterators can be used.

static BreakIterator getCharacterInstance(ULocale where)

[icu] Returns a new instance of BreakIterator that locates logical-character boundaries.

static BreakIterator getCharacterInstance(Locale where)

Returns a new instance of BreakIterator that locates logical-character boundaries.

static BreakIterator getCharacterInstance()

Returns a new instance of BreakIterator that locates logical-character boundaries.

static BreakIterator getLineInstance(Locale where)

Returns a new instance of BreakIterator that locates legal line- wrapping positions.

static BreakIterator getLineInstance(ULocale where)

[icu] Returns a new instance of BreakIterator that locates legal line- wrapping positions.

static BreakIterator getLineInstance()

Returns a new instance of BreakIterator that locates legal line- wrapping positions.

int getRuleStatus()

For RuleBasedBreakIterators, return the status tag from the break rule that determined the most recently returned break position.

int getRuleStatusVec(int[] fillInArray)

For RuleBasedBreakIterators, get the status (tag) values from the break rule(s) that determined the most recently returned break position.

static BreakIterator getSentenceInstance(Locale where)

Returns a new instance of BreakIterator that locates sentence boundaries.

static BreakIterator getSentenceInstance(ULocale where)

[icu] Returns a new instance of BreakIterator that locates sentence boundaries.

static BreakIterator getSentenceInstance()

Returns a new instance of BreakIterator that locates sentence boundaries.

abstract CharacterIterator getText()

Returns a CharacterIterator over the text being analyzed.

static BreakIterator getTitleInstance(Locale where)

[icu] Returns a new instance of BreakIterator that locates title boundaries.

static BreakIterator getTitleInstance(ULocale where)

[icu] Returns a new instance of BreakIterator that locates title boundaries.

static BreakIterator getTitleInstance()

[icu] Returns a new instance of BreakIterator that locates title boundaries.

static BreakIterator getWordInstance(Locale where)

Returns a new instance of BreakIterator that locates word boundaries.

static BreakIterator getWordInstance(ULocale where)

[icu] Returns a new instance of BreakIterator that locates word boundaries.

static BreakIterator getWordInstance()

Returns a new instance of BreakIterator that locates word boundaries.

boolean isBoundary(int offset)

Return true if the specified position is a boundary position.

abstract int last()

Set the iterator to the last boundary position.

abstract int next()

Advances the iterator forward one boundary.

abstract int next(int n)

Move the iterator by the specified number of steps in the text.

int preceding(int offset)

Sets the iterator's current iteration position to be the last boundary position preceding the specified position.

abstract int previous()

Move the iterator backward one boundary.

void setText(String newText)

Sets the iterator to analyze a new piece of text.

abstract void setText(CharacterIterator newText)

Sets the iterator to analyze a new piece of text.

Inherited methods

Constants

DONE

added in API level 24
public static final int DONE

DONE is returned by previous() and next() after all valid boundaries have been returned.

Constant Value: -1 (0xffffffff)

KIND_CHARACTER

added in API level 24
public static final int KIND_CHARACTER

[icu]

Constant Value: 0 (0x00000000)

KIND_LINE

added in API level 24
public static final int KIND_LINE

[icu]

Constant Value: 2 (0x00000002)

KIND_SENTENCE

added in API level 24
public static final int KIND_SENTENCE

[icu]

Constant Value: 3 (0x00000003)

KIND_TITLE

added in API level 24
public static final int KIND_TITLE

[icu]

Constant Value: 4 (0x00000004)

KIND_WORD

added in API level 24
public static final int KIND_WORD

[icu]

Constant Value: 1 (0x00000001)

WORD_IDEO

added in API level 24
public static final int WORD_IDEO

Tag value for words containing ideographic characters, lower limit

Constant Value: 400 (0x00000190)

WORD_IDEO_LIMIT

added in API level 24
public static final int WORD_IDEO_LIMIT

Tag value for words containing ideographic characters, upper limit

Constant Value: 500 (0x000001f4)

WORD_KANA

added in API level 24
public static final int WORD_KANA

Tag value for words containing kana characters, lower limit

Constant Value: 300 (0x0000012c)

WORD_KANA_LIMIT

added in API level 24
public static final int WORD_KANA_LIMIT

Tag value for words containing kana characters, upper limit

Constant Value: 400 (0x00000190)

WORD_LETTER

added in API level 24
public static final int WORD_LETTER

Tag value for words that contain letters, excluding hiragana, katakana or ideographic characters, lower limit.

Constant Value: 200 (0x000000c8)

WORD_LETTER_LIMIT

added in API level 24
public static final int WORD_LETTER_LIMIT

Tag value for words containing letters, upper limit

Constant Value: 300 (0x0000012c)

WORD_NONE

added in API level 24
public static final int WORD_NONE

Tag value for "words" that do not fit into any of other categories. Includes spaces and most punctuation.

Constant Value: 0 (0x00000000)

WORD_NONE_LIMIT

added in API level 24
public static final int WORD_NONE_LIMIT

Upper bound for tags for uncategorized words.

Constant Value: 100 (0x00000064)

WORD_NUMBER

added in API level 24
public static final int WORD_NUMBER

Tag value for words that appear to be numbers, lower limit.

Constant Value: 100 (0x00000064)

WORD_NUMBER_LIMIT

added in API level 24
public static final int WORD_NUMBER_LIMIT

Tag value for words that appear to be numbers, upper limit.

Constant Value: 200 (0x000000c8)

Protected constructors

BreakIterator

added in API level 24
protected BreakIterator ()

Default constructor. There is no state that is carried by this abstract base class.

Public methods

clone

added in API level 24
public Object clone ()

Clone method. Creates another BreakIterator with the same behavior and current state as this one.

Returns
Object The clone.

current

added in API level 24
public abstract int current ()

Return the iterator's current position.

Returns
int The iterator's current position.

first

added in API level 24
public abstract int first ()

Set the iterator to the first boundary position. This is always the beginning index of the text this iterator iterates over. For example, if the iterator iterates over a whole string, this function will always return 0.

Returns
int The character offset of the beginning of the stretch of text being broken.

following

added in API level 24
public abstract int following (int offset)

Sets the iterator's current iteration position to be the first boundary position following the specified position. (Whether the specified position is itself a boundary position or not doesn't matter-- this function always moves the iteration position to the first boundary after the specified position.) If the specified position is the past-the-end position, returns DONE.

Parameters
offset int: The character position to start searching from.

Returns
int The position of the first boundary position following "offset" (whether or not "offset" itself is a boundary position), or DONE if "offset" is the past-the-end offset.

getAvailableLocales

added in API level 24
public static Locale[] getAvailableLocales ()

Returns a list of locales for which BreakIterators can be used.

Returns
Locale[] An array of Locales. All of the locales in the array can be used when creating a BreakIterator.

getCharacterInstance

added in API level 24
public static BreakIterator getCharacterInstance (ULocale where)

[icu] Returns a new instance of BreakIterator that locates logical-character boundaries.

Parameters
where ULocale: A Locale specifying the language of the text being analyzed.

Returns
BreakIterator A new instance of BreakIterator that locates logical-character boundaries.

Throws
NullPointerException if where is null.

getCharacterInstance

added in API level 24
public static BreakIterator getCharacterInstance (Locale where)

Returns a new instance of BreakIterator that locates logical-character boundaries.

Parameters
where Locale: A Locale specifying the language of the text being analyzed.

Returns
BreakIterator A new instance of BreakIterator that locates logical-character boundaries.

Throws
NullPointerException if where is null.

getCharacterInstance

added in API level 24
public static BreakIterator getCharacterInstance ()

Returns a new instance of BreakIterator that locates logical-character boundaries. This function assumes that the text being analyzed is in the default locale's language.

Returns
BreakIterator A new instance of BreakIterator that locates logical-character boundaries.

getLineInstance

added in API level 24
public static BreakIterator getLineInstance (Locale where)

Returns a new instance of BreakIterator that locates legal line- wrapping positions.

Parameters
where Locale: A Locale specifying the language of the text being broken.

Returns
BreakIterator A new instance of BreakIterator that locates legal line-wrapping positions.

Throws
NullPointerException if where is null.

getLineInstance

added in API level 24
public static BreakIterator getLineInstance (ULocale where)

[icu] Returns a new instance of BreakIterator that locates legal line- wrapping positions.

Parameters
where ULocale: A Locale specifying the language of the text being broken.

Returns
BreakIterator A new instance of BreakIterator that locates legal line-wrapping positions.

Throws
NullPointerException if where is null.

getLineInstance

added in API level 24
public static BreakIterator getLineInstance ()

Returns a new instance of BreakIterator that locates legal line- wrapping positions. This function assumes the text being broken is in the default locale's language.

Returns
BreakIterator A new instance of BreakIterator that locates legal line-wrapping positions.

getRuleStatus

added in API level 24
public int getRuleStatus ()

For RuleBasedBreakIterators, return the status tag from the break rule that determined the most recently returned break position.

For break iterator types that do not support a rule status, a default value of 0 is returned.

Returns
int The status from the break rule that determined the most recently returned break position.

getRuleStatusVec

added in API level 24
public int getRuleStatusVec (int[] fillInArray)

For RuleBasedBreakIterators, get the status (tag) values from the break rule(s) that determined the most recently returned break position.

For break iterator types that do not support rule status, no values are returned.

If the size of the output array is insufficient to hold the data, the output will be truncated to the available length. No exception will be thrown.

Parameters
fillInArray int: an array to be filled in with the status values.

Returns
int The number of rule status values from rules that determined the most recent boundary returned by the break iterator. In the event that the array is too small, the return value is the total number of status values that were available, not the reduced number that were actually returned.

getSentenceInstance

added in API level 24
public static BreakIterator getSentenceInstance (Locale where)

Returns a new instance of BreakIterator that locates sentence boundaries.

Parameters
where Locale: A Locale specifying the language of the text being analyzed.

Returns
BreakIterator A new instance of BreakIterator that locates sentence boundaries.

Throws
NullPointerException if where is null.

getSentenceInstance

added in API level 24
public static BreakIterator getSentenceInstance (ULocale where)

[icu] Returns a new instance of BreakIterator that locates sentence boundaries.

Parameters
where ULocale: A Locale specifying the language of the text being analyzed.

Returns
BreakIterator A new instance of BreakIterator that locates sentence boundaries.

Throws
NullPointerException if where is null.

getSentenceInstance

added in API level 24
public static BreakIterator getSentenceInstance ()

Returns a new instance of BreakIterator that locates sentence boundaries. This function assumes the text being analyzed is in the default locale's language.

Returns
BreakIterator A new instance of BreakIterator that locates sentence boundaries.

getText

added in API level 24
public abstract CharacterIterator getText ()

Returns a CharacterIterator over the text being analyzed. For at least some subclasses of BreakIterator, this is a reference to the actual iterator being used by the BreakIterator, and therefore, this function's return value should be treated as const. No guarantees are made about the current position of this iterator when it is returned. If you need to move that position to examine the text, clone this function's return value first.

Returns
CharacterIterator A CharacterIterator over the text being analyzed.

getTitleInstance

added in API level 24
public static BreakIterator getTitleInstance (Locale where)

[icu] Returns a new instance of BreakIterator that locates title boundaries. The iterator returned locates title boundaries as described for Unicode 3.2 only. For Unicode 4.0 and above title boundary iteration, please use Word Boundary iterator.getWordInstance()

Parameters
where Locale: A Locale specifying the language of the text being analyzed.

Returns
BreakIterator A new instance of BreakIterator that locates title boundaries.

Throws
NullPointerException if where is null.

getTitleInstance

added in API level 24
public static BreakIterator getTitleInstance (ULocale where)

[icu] Returns a new instance of BreakIterator that locates title boundaries. The iterator returned locates title boundaries as described for Unicode 3.2 only. For Unicode 4.0 and above title boundary iteration, please use Word Boundary iterator.getWordInstance()

Parameters
where ULocale: A Locale specifying the language of the text being analyzed.

Returns
BreakIterator A new instance of BreakIterator that locates title boundaries.

Throws
NullPointerException if where is null.

getTitleInstance

added in API level 24
public static BreakIterator getTitleInstance ()

[icu] Returns a new instance of BreakIterator that locates title boundaries. This function assumes the text being analyzed is in the default locale's language. The iterator returned locates title boundaries as described for Unicode 3.2 only. For Unicode 4.0 and above title boundary iteration, please use a word boundary iterator. getWordInstance()

Returns
BreakIterator A new instance of BreakIterator that locates title boundaries.

getWordInstance

added in API level 24
public static BreakIterator getWordInstance (Locale where)

Returns a new instance of BreakIterator that locates word boundaries.

Parameters
where Locale: A locale specifying the language of the text to be analyzed.

Returns
BreakIterator An instance of BreakIterator that locates word boundaries.

Throws
NullPointerException if where is null.

getWordInstance

added in API level 24
public static BreakIterator getWordInstance (ULocale where)

[icu] Returns a new instance of BreakIterator that locates word boundaries.

Parameters
where ULocale: A locale specifying the language of the text to be analyzed.

Returns
BreakIterator An instance of BreakIterator that locates word boundaries.

Throws
NullPointerException if where is null.

getWordInstance

added in API level 24
public static BreakIterator getWordInstance ()

Returns a new instance of BreakIterator that locates word boundaries. This function assumes that the text being analyzed is in the default locale's language.

Returns
BreakIterator An instance of BreakIterator that locates word boundaries.

isBoundary

added in API level 24
public boolean isBoundary (int offset)

Return true if the specified position is a boundary position. If the function returns true, the current iteration position is set to the specified position; if the function returns false, the current iteration position is set as though following() had been called.

Parameters
offset int: the offset to check.

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

last

added in API level 24
public abstract int last ()

Set the iterator to the last boundary position. This is always the "past-the-end" index of the text this iterator iterates over. For example, if the iterator iterates over a whole string (call it "text"), this function will always return text.length().

Returns
int The character offset of the end of the stretch of text being broken.

next

added in API level 24
public abstract int next ()

Advances the iterator forward one boundary. The current iteration position is updated to point to the next boundary position after the current position, and this is also the value that is returned. If the current position is equal to the value returned by last(), or to DONE, this function returns DONE and sets the current position to DONE.

Returns
int The position of the first boundary position following the iteration position.

next

added in API level 24
public abstract int next (int n)

Move the iterator by the specified number of steps in the text. A positive number moves the iterator forward; a negative number moves the iterator backwards. If this causes the iterator to move off either end of the text, this function returns DONE; otherwise, this function returns the position of the appropriate boundary. Calling this function is equivalent to calling next() or previous() n times.

Parameters
n int: The number of boundaries to advance over (if positive, moves forward; if negative, moves backwards).

Returns
int The position of the boundary n boundaries from the current iteration position, or DONE if moving n boundaries causes the iterator to advance off either end of the text.

preceding

added in API level 24
public int preceding (int offset)

Sets the iterator's current iteration position to be the last boundary position preceding the specified position. (Whether the specified position is itself a boundary position or not doesn't matter-- this function always moves the iteration position to the last boundary before the specified position.) If the specified position is the starting position, returns DONE.

Parameters
offset int: The character position to start searching from.

Returns
int The position of the last boundary position preceding "offset" (whether of not "offset" itself is a boundary position), or DONE if "offset" is the starting offset of the iterator.

previous

added in API level 24
public abstract int previous ()

Move the iterator backward one boundary. The current iteration position is updated to point to the last boundary position before the current position, and this is also the value that is returned. If the current position is equal to the value returned by first(), or to DONE, this function returns DONE and sets the current position to DONE.

Returns
int The position of the last boundary position preceding the iteration position.

setText

added in API level 24
public void setText (String newText)

Sets the iterator to analyze a new piece of text. The new piece of text is passed in as a String, and the current iteration position is reset to the beginning of the string. (The old text is dropped.)

Parameters
newText String: A String containing the text to analyze with this BreakIterator.

setText

added in API level 24
public abstract void setText (CharacterIterator newText)

Sets the iterator to analyze a new piece of text. The BreakIterator is passed a CharacterIterator through which it will access the text itself. The current iteration position is reset to the CharacterIterator's start index. (The old iterator is dropped.)

Parameters
newText CharacterIterator: A CharacterIterator referring to the text to analyze with this BreakIterator (the iterator's current position is ignored, but its other state is significant).