- java.lang.Object
-
- java.text.BreakIterator
-
- All Implemented Interfaces:
Cloneable
public abstract class BreakIterator extends Object implements Cloneable
TheBreakIteratorclass implements methods for finding the location of boundaries in text. Instances ofBreakIteratormaintain a current position and scan over text returning the index of characters where boundaries occur. Internally,BreakIteratorscans text using aCharacterIterator, and is thus able to scan text held by any object implementing that protocol. AStringCharacterIteratoris used to scanStringobjects passed tosetText.You use the factory methods provided by this class to create instances of various types of break iterators. In particular, use
getWordInstance,getLineInstance,getSentenceInstance, andgetCharacterInstanceto createBreakIterators that perform word, line, sentence, and character boundary analysis respectively. A singleBreakIteratorcan work only on one unit (word, line, sentence, and so on). You must use a different iterator for each unit boundary analysis you wish to perform.Line boundary analysis determines where a text string can be broken when line-wrapping. The mechanism correctly handles punctuation and hyphenated words. Actual line breaking needs to also consider the available line width and is handled by higher-level software.
Sentence boundary analysis allows selection with correct interpretation of periods within numbers and abbreviations, and trailing punctuation marks such as quotation marks and parentheses.
Word boundary analysis is used by search and replace functions, as well as within text editing applications that allow the user to select words with a double click. Word selection provides correct interpretation of punctuation marks within and following words. Characters that are not part of a word, such as symbols or punctuation marks, have word-breaks on both sides.
Character boundary analysis allows users to interact with characters as they expect to, for example, when moving the cursor through a text string. Character boundary analysis provides correct navigation through character strings, regardless of how the character is stored. The boundaries returned may be those of supplementary characters, combining character sequences, or ligature clusters. For example, an accented character might be stored as a base character and a diacritical mark. What users consider to be a character can differ between languages.
The
BreakIteratorinstances returned by the factory methods of this class are intended for use with natural languages only, not for programming language text. It is however possible to define subclasses that tokenize a programming language.Examples:
Creating and using text boundaries:
Print each element in order: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 reverse 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 first element: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 last 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 the element at a specified position:public static void printLast(BreakIterator boundary, String source) { int end = boundary.last(); int start = boundary.previous(); System.out.println(source.substring(start,end)); }
Find the next word: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)); }
(The iterator returned by BreakIterator.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 a simple heuristic to determine which boundary is the beginning of a word: If the characters between this boundary and the next boundary include at least one letter (this can be an alphabetical letter, a CJK ideograph, a Hangul syllable, a Kana character, etc.), then the text between this boundary and the next is a word; otherwise, it's the material between words.)public static int nextWordStartAfter(int pos, String text) { BreakIterator wb = BreakIterator.getWordInstance(); wb.setText(text); int last = wb.following(pos); int current = wb.next(); while (current != BreakIterator.DONE) { for (int p = last; p < current; p++) { if (Character.isLetter(text.codePointAt(p))) return last; } last = current; current = wb.next(); } return BreakIterator.DONE; }- Since:
- 1.1
- See Also:
CharacterIterator
-
-
Field Summary
Fields Modifier and Type Field Description static intDONEDONE is returned by previous(), next(), next(int), preceding(int) and following(int) when either the first or last text boundary has been reached.
-
Constructor Summary
Constructors Modifier Constructor Description protectedBreakIterator()Constructor.
-
Method Summary
All Methods Static Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description Objectclone()Create a copy of this iteratorabstract intcurrent()Returns character index of the text boundary that was most recently returned by next(), next(int), previous(), first(), last(), following(int) or preceding(int).abstract intfirst()Returns the first boundary.abstract intfollowing(int offset)Returns the first boundary following the specified character offset.static Locale[]getAvailableLocales()Returns an array of all locales for which theget*Instancemethods of this class can return localized instances.static BreakIteratorgetCharacterInstance()static BreakIteratorgetCharacterInstance(Locale locale)Returns a newBreakIteratorinstance for character breaks for the given locale.static BreakIteratorgetLineInstance()static BreakIteratorgetLineInstance(Locale locale)Returns a newBreakIteratorinstance for line breaks for the given locale.static BreakIteratorgetSentenceInstance()static BreakIteratorgetSentenceInstance(Locale locale)Returns a newBreakIteratorinstance for sentence breaks for the given locale.abstract CharacterIteratorgetText()Get the text being scannedstatic BreakIteratorgetWordInstance()static BreakIteratorgetWordInstance(Locale locale)Returns a newBreakIteratorinstance for word breaks for the given locale.booleanisBoundary(int offset)Returns true if the specified character offset is a text boundary.abstract intlast()Returns the last boundary.abstract intnext()Returns the boundary following the current boundary.abstract intnext(int n)Returns the nth boundary from the current boundary.intpreceding(int offset)Returns the last boundary preceding the specified character offset.abstract intprevious()Returns the boundary preceding the current boundary.voidsetText(String newText)Set a new text string to be scanned.abstract voidsetText(CharacterIterator newText)Set a new text for scanning.
-
-
-
Field Detail
-
DONE
public static final int DONE
DONE is returned by previous(), next(), next(int), preceding(int) and following(int) when either the first or last text boundary has been reached.- See Also:
- Constant Field Values
-
-
Method Detail
-
clone
public Object clone()
Create a copy of this iterator
-
first
public abstract int first()
Returns the first boundary. The iterator's current position is set to the first text boundary.- Returns:
- The character index of the first text boundary.
-
last
public abstract int last()
Returns the last boundary. The iterator's current position is set to the last text boundary.- Returns:
- The character index of the last text boundary.
-
next
public abstract int next(int n)
Returns the nth boundary from the current boundary. If either the first or last text boundary has been reached, it returnsBreakIterator.DONEand the current position is set to either the first or last text boundary depending on which one is reached. Otherwise, the iterator's current position is set to the new boundary. For example, if the iterator's current position is the mth text boundary and three more boundaries exist from the current boundary to the last text boundary, the next(2) call will return m + 2. The new text position is set to the (m + 2)th text boundary. A next(4) call would returnBreakIterator.DONEand the last text boundary would become the new text position.- Parameters:
n- which boundary to return. A value of 0 does nothing. Negative values move to previous boundaries and positive values move to later boundaries.- Returns:
- The character index of the nth boundary from the current position
or
BreakIterator.DONEif either first or last text boundary has been reached.
-
next
public abstract int next()
Returns the boundary following the current boundary. If the current boundary is the last text boundary, it returnsBreakIterator.DONEand the iterator's current position is unchanged. Otherwise, the iterator's current position is set to the boundary following the current boundary.- Returns:
- The character index of the next text boundary or
BreakIterator.DONEif the current boundary is the last text boundary. Equivalent to next(1). - See Also:
next(int)
-
previous
public abstract int previous()
Returns the boundary preceding the current boundary. If the current boundary is the first text boundary, it returnsBreakIterator.DONEand the iterator's current position is unchanged. Otherwise, the iterator's current position is set to the boundary preceding the current boundary.- Returns:
- The character index of the previous text boundary or
BreakIterator.DONEif the current boundary is the first text boundary.
-
following
public abstract int following(int offset)
Returns the first boundary following the specified character offset. If the specified offset equals to the last text boundary, it returnsBreakIterator.DONEand the iterator's current position is unchanged. Otherwise, the iterator's current position is set to the returned boundary. The value returned is always greater than the offset or the valueBreakIterator.DONE.- Parameters:
offset- the character offset to begin scanning.- Returns:
- The first boundary after the specified offset or
BreakIterator.DONEif the last text boundary is passed in as the offset. - Throws:
IllegalArgumentException- if the specified offset is less than the first text boundary or greater than the last text boundary.
-
preceding
public int preceding(int offset)
Returns the last boundary preceding the specified character offset. If the specified offset equals to the first text boundary, it returnsBreakIterator.DONEand the iterator's current position is unchanged. Otherwise, the iterator's current position is set to the returned boundary. The value returned is always less than the offset or the valueBreakIterator.DONE.- Parameters:
offset- the character offset to begin scanning.- Returns:
- The last boundary before the specified offset or
BreakIterator.DONEif the first text boundary is passed in as the offset. - Throws:
IllegalArgumentException- if the specified offset is less than the first text boundary or greater than the last text boundary.- Since:
- 1.2
-
isBoundary
public boolean isBoundary(int offset)
Returns true if the specified character offset is a text boundary.- Parameters:
offset- the character offset to check.- Returns:
trueif "offset" is a boundary position,falseotherwise.- Throws:
IllegalArgumentException- if the specified offset is less than the first text boundary or greater than the last text boundary.- Since:
- 1.2
-
current
public abstract int current()
Returns character index of the text boundary that was most recently returned by next(), next(int), previous(), first(), last(), following(int) or preceding(int). If any of these methods returnsBreakIterator.DONEbecause either first or last text boundary has been reached, it returns the first or last text boundary depending on which one is reached.- Returns:
- The text boundary returned from the above methods, first or last text boundary.
- See Also:
next(),next(int),previous(),first(),last(),following(int),preceding(int)
-
getText
public abstract CharacterIterator getText()
Get the text being scanned- Returns:
- the text being scanned
-
setText
public void setText(String newText)
Set a new text string to be scanned. The current scan position is reset to first().- Parameters:
newText- new text to scan.
-
setText
public abstract void setText(CharacterIterator newText)
Set a new text for scanning. The current scan position is reset to first().- Parameters:
newText- new text to scan.
-
getWordInstance
public static BreakIterator getWordInstance()
- Returns:
- A break iterator for word breaks
-
getWordInstance
public static BreakIterator getWordInstance(Locale locale)
Returns a newBreakIteratorinstance for word breaks for the given locale.- Parameters:
locale- the desired locale- Returns:
- A break iterator for word breaks
- Throws:
NullPointerException- iflocaleis null
-
getLineInstance
public static BreakIterator getLineInstance()
- Returns:
- A break iterator for line breaks
-
getLineInstance
public static BreakIterator getLineInstance(Locale locale)
Returns a newBreakIteratorinstance for line breaks for the given locale.- Parameters:
locale- the desired locale- Returns:
- A break iterator for line breaks
- Throws:
NullPointerException- iflocaleis null
-
getCharacterInstance
public static BreakIterator getCharacterInstance()
- Returns:
- A break iterator for character breaks
-
getCharacterInstance
public static BreakIterator getCharacterInstance(Locale locale)
Returns a newBreakIteratorinstance for character breaks for the given locale.- Parameters:
locale- the desired locale- Returns:
- A break iterator for character breaks
- Throws:
NullPointerException- iflocaleis null
-
getSentenceInstance
public static BreakIterator getSentenceInstance()
- Returns:
- A break iterator for sentence breaks
-
getSentenceInstance
public static BreakIterator getSentenceInstance(Locale locale)
Returns a newBreakIteratorinstance for sentence breaks for the given locale.- Parameters:
locale- the desired locale- Returns:
- A break iterator for sentence breaks
- Throws:
NullPointerException- iflocaleis null
-
getAvailableLocales
public static Locale[] getAvailableLocales()
Returns an array of all locales for which theget*Instancemethods of this class can return localized instances. The returned array represents the union of locales supported by the Java runtime and by installedBreakIteratorProviderimplementations. It must contain at least aLocaleinstance equal toLocale.US.- Returns:
- An array of locales for which localized
BreakIteratorinstances are available.
-
-