Class BreakIterator

java.lang.Object
org.graalvm.shadowed.com.ibm.icu.text.BreakIterator
All Implemented Interfaces:
Cloneable
Direct Known Subclasses:
RuleBasedBreakIterator, SimpleFilteredSentenceBreakIterator
public abstract class BreakIterator extends Object implements Cloneable
.

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. 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:

  • Field Details

    • DONE

      public static final int DONE
      DONE is returned by previous() and next() after all valid boundaries have been returned.
      See Also:

    • WORD_NONE

      public static final int WORD_NONE
      Tag value for "words" that do not fit into any of other categories. Includes spaces and most punctuation.
      See Also:

    • WORD_NONE_LIMIT

      public static final int WORD_NONE_LIMIT
      Upper bound for tags for uncategorized words.
      See Also:

    • WORD_NUMBER

      public static final int WORD_NUMBER
      Tag value for words that appear to be numbers, lower limit.
      See Also:

    • WORD_NUMBER_LIMIT

      public static final int WORD_NUMBER_LIMIT
      Tag value for words that appear to be numbers, upper limit.
      See Also:

    • WORD_LETTER

      public static final int WORD_LETTER
      Tag value for words that contain letters, excluding hiragana, katakana or ideographic characters, lower limit.
      See Also:

    • WORD_LETTER_LIMIT

      public static final int WORD_LETTER_LIMIT
      Tag value for words containing letters, upper limit
      See Also:

    • WORD_KANA

      public static final int WORD_KANA
      Tag value for words containing kana characters, lower limit
      See Also:

    • WORD_KANA_LIMIT

      public static final int WORD_KANA_LIMIT
      Tag value for words containing kana characters, upper limit
      See Also:

    • WORD_IDEO

      public static final int WORD_IDEO
      Tag value for words containing ideographic characters, lower limit
      See Also:

    • WORD_IDEO_LIMIT

      public static final int WORD_IDEO_LIMIT
      Tag value for words containing ideographic characters, upper limit
      See Also:

    • KIND_CHARACTER

      public static final int KIND_CHARACTER
      See Also:

    • KIND_WORD

      public static final int KIND_WORD
      See Also:

    • KIND_LINE

      public static final int KIND_LINE
      See Also:

    • KIND_SENTENCE

      public static final int KIND_SENTENCE
      See Also:

    • KIND_TITLE

      @Deprecated public static final int KIND_TITLE
      Deprecated.
      ICU 64 Use getWordInstance() instead.
      See Also:

  • Constructor Details

    • BreakIterator

      protected BreakIterator()
      Default constructor. There is no state that is carried by this abstract base class.

  • Method Details

    • clone

      public Object clone()
      Clone method. Creates another BreakIterator with the same behavior and current state as this one.
      Overrides:
      clone in class Object
      Returns:
      The clone.

    • first

      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:
      The character offset of the beginning of the stretch of text being broken.

    • last

      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:
      The character offset of the end of the stretch of text being broken.

    • next

      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 - The number of boundaries to advance over (if positive, moves forward; if negative, moves backwards).
      Returns:
      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.

    • next

      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:
      The position of the first boundary position following the iteration position.

    • previous

      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:
      The position of the last boundary position preceding the iteration position.

    • following

      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 - The character position to start searching from.
      Returns:
      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.

    • preceding

      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 - The character position to start searching from.
      Returns:
      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.

    • isBoundary

      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 - the offset to check.
      Returns:
      True if "offset" is a boundary position.

    • current

      public abstract int current()
      Return the iterator's current position.
      Returns:
      The iterator's current position.

    • getRuleStatus

      public int getRuleStatus()
      For RuleBasedBreakIterators, return the status tag from the break rule that determined the boundary at the current iteration position.

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

      Returns:
      The status from the break rule that determined the boundary at the current iteration position.

    • getRuleStatusVec

      public int getRuleStatusVec(int[] fillInArray)
      For RuleBasedBreakIterators, get the status (tag) values from the break rule(s) that determined the the boundary at the current iteration 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 - an array to be filled in with the status values.
      Returns:
      The number of rule status values from rules that determined the the boundary at the current iteration position. 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.

    • getText

      public abstract CharacterIterator getText()
      Returns a CharacterIterator over the text being analyzed.

      Caution:The state of the returned CharacterIterator must not be modified in any way while the BreakIterator is still in use. Doing so will lead to undefined behavior of the BreakIterator. Clone the returned CharacterIterator first and work with that.

      The returned CharacterIterator is a reference to the actual iterator being used by the BreakIterator. No guarantees are made about the current position of this iterator when it is returned; it may differ from the BreakIterators current position. If you need to move that position to examine the text, clone this function's return value first.

      Returns:
      A CharacterIterator over the text being analyzed.

    • setText

      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 - A String containing the text to analyze with this BreakIterator.

    • setText

      public void setText(CharSequence newText)
      Sets the iterator to analyze a new piece of text. The new piece of text is passed in as a CharSequence, and the current iteration position is reset to the beginning of the text. (The old text is dropped.)

      The text underlying the CharSequence must not be be modified while the BreakIterator holds a references to it. (As could possibly occur with a StringBuilder, for example).

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

    • setText

      public abstract void setText(CharacterIterator newText)
      Sets the iterator to analyze a new piece of text. This function resets the current iteration position to the beginning of the text. (The old iterator is dropped.)

      Caution: The supplied CharacterIterator is used directly by the BreakIterator, and must not be altered in any way by code outside of the BreakIterator. Doing so will lead to undefined behavior of the BreakIterator.

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

    • getWordInstance

      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:
      An instance of BreakIterator that locates word boundaries.

    • getWordInstance

      public static BreakIterator getWordInstance(Locale where)
      Returns a new instance of BreakIterator that locates word boundaries.
      Parameters:
      where - A locale specifying the language of the text to be analyzed.
      Returns:
      An instance of BreakIterator that locates word boundaries.
      Throws:
      NullPointerException - if where is null.

    • getWordInstance

      public static BreakIterator getWordInstance(ULocale where)
      Returns a new instance of BreakIterator that locates word boundaries.
      Parameters:
      where - A locale specifying the language of the text to be analyzed.
      Returns:
      An instance of BreakIterator that locates word boundaries.
      Throws:
      NullPointerException - if where is null.

    • getLineInstance

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

    • getLineInstance

      public static BreakIterator getLineInstance(Locale where)
      Returns a new instance of BreakIterator that locates legal line- wrapping positions.
      Parameters:
      where - A Locale specifying the language of the text being broken.
      Returns:
      A new instance of BreakIterator that locates legal line-wrapping positions.
      Throws:
      NullPointerException - if where is null.

    • getLineInstance

      public static BreakIterator getLineInstance(ULocale where)
      Returns a new instance of BreakIterator that locates legal line- wrapping positions.
      Parameters:
      where - A Locale specifying the language of the text being broken.
      Returns:
      A new instance of BreakIterator that locates legal line-wrapping positions.
      Throws:
      NullPointerException - if where is null.

    • getCharacterInstance

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

    • getCharacterInstance

      public static BreakIterator getCharacterInstance(Locale where)
      Returns a new instance of BreakIterator that locates logical-character boundaries.
      Parameters:
      where - A Locale specifying the language of the text being analyzed.
      Returns:
      A new instance of BreakIterator that locates logical-character boundaries.
      Throws:
      NullPointerException - if where is null.

    • getCharacterInstance

      public static BreakIterator getCharacterInstance(ULocale where)
      Returns a new instance of BreakIterator that locates logical-character boundaries.
      Parameters:
      where - A Locale specifying the language of the text being analyzed.
      Returns:
      A new instance of BreakIterator that locates logical-character boundaries.
      Throws:
      NullPointerException - if where is null.

    • getSentenceInstance

      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:
      A new instance of BreakIterator that locates sentence boundaries.

    • getSentenceInstance

      public static BreakIterator getSentenceInstance(Locale where)
      Returns a new instance of BreakIterator that locates sentence boundaries.
      Parameters:
      where - A Locale specifying the language of the text being analyzed.
      Returns:
      A new instance of BreakIterator that locates sentence boundaries.
      Throws:
      NullPointerException - if where is null.

    • getSentenceInstance

      public static BreakIterator getSentenceInstance(ULocale where)
      Returns a new instance of BreakIterator that locates sentence boundaries.
      Parameters:
      where - A Locale specifying the language of the text being analyzed.
      Returns:
      A new instance of BreakIterator that locates sentence boundaries.
      Throws:
      NullPointerException - if where is null.

    • getTitleInstance

      @Deprecated public static BreakIterator getTitleInstance()
      Deprecated.
      ICU 64 Use getWordInstance() instead.
      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:
      A new instance of BreakIterator that locates title boundaries.

    • getTitleInstance

      @Deprecated public static BreakIterator getTitleInstance(Locale where)
      Deprecated.
      ICU 64 Use getWordInstance() instead.
      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 - A Locale specifying the language of the text being analyzed.
      Returns:
      A new instance of BreakIterator that locates title boundaries.
      Throws:
      NullPointerException - if where is null.

    • getTitleInstance

      @Deprecated public static BreakIterator getTitleInstance(ULocale where)
      Deprecated.
      ICU 64 Use getWordInstance() instead.
      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 - A Locale specifying the language of the text being analyzed.
      Returns:
      A new instance of BreakIterator that locates title boundaries.
      Throws:
      NullPointerException - if where is null.

    • registerInstance

      public static Object registerInstance(BreakIterator iter, Locale locale, int kind)
      Registers a new break iterator of the indicated kind, to use in the given locale. Clones of the iterator will be returned if a request for a break iterator of the given kind matches or falls back to this locale.

      Because ICU may choose to cache BreakIterator objects internally, this must be called at application startup, prior to any calls to BreakIterator.getInstance to avoid undefined behavior.

      Parameters:
      iter - the BreakIterator instance to adopt.
      locale - the Locale for which this instance is to be registered
      kind - the type of iterator for which this instance is to be registered
      Returns:
      a registry key that can be used to unregister this instance

    • registerInstance

      public static Object registerInstance(BreakIterator iter, ULocale locale, int kind)
      Registers a new break iterator of the indicated kind, to use in the given locale. Clones of the iterator will be returned if a request for a break iterator of the given kind matches or falls back to this locale.

      Because ICU may choose to cache BreakIterator objects internally, this must be called at application startup, prior to any calls to BreakIterator.getInstance to avoid undefined behavior.

      Parameters:
      iter - the BreakIterator instance to adopt.
      locale - the Locale for which this instance is to be registered
      kind - the type of iterator for which this instance is to be registered
      Returns:
      a registry key that can be used to unregister this instance

    • unregister

      public static boolean unregister(Object key)
      Unregisters a previously-registered BreakIterator using the key returned from the register call. Key becomes invalid after this call and should not be used again.
      Parameters:
      key - the registry key returned by a previous call to registerInstance
      Returns:
      true if the iterator for the key was successfully unregistered

    • getBreakInstance

      @Deprecated public static BreakIterator getBreakInstance(ULocale where, int kind)
      Deprecated.
      This API is ICU internal only.
      Returns a particular kind of BreakIterator for a locale. Avoids writing a switch statement with getXYZInstance(where) calls.

    • getAvailableLocales

      public static Locale[] getAvailableLocales()
      Returns a list of locales for which BreakIterators can be used.
      Returns:
      An array of Locales. All of the locales in the array can be used when creating a BreakIterator.

    • getAvailableULocales

      public static ULocale[] getAvailableULocales()
      Returns a list of locales for which BreakIterators can be used.
      Returns:
      An array of Locales. All of the locales in the array can be used when creating a BreakIterator.

    • getLocale

      public final ULocale getLocale(ULocale.Type type)
      Returns the locale that was used to create this object, or null. This may may differ from the locale requested at the time of this object's creation. For example, if an object is created for locale en_US_CALIFORNIA, the actual data may be drawn from en (the actual locale), and en_US may be the most specific locale that exists (the valid locale).

      Note: The actual locale is returned correctly, but the valid locale is not, in most cases.

      Parameters:
      type - type of information requested, either ULocale.VALID_LOCALE or ULocale.ACTUAL_LOCALE.
      Returns:
      the information specified by type, or null if this object was not constructed from locale data.
      See Also: