java.lang.Object java.text.BreakIterator
public abstract class BreakIterator
The BreakIterator class implements methods for finding the location of boundaries in text. Instances of BreakIterator maintain a current position and scan over text returning the index of characters where boundaries occur. Internally, BreakIterator scans text using a CharacterIterator, and is thus able to scan text held by any object implementing that protocol. A StringCharacterIterator is used to scan String objects passed to setText.
You use the factory methods provided by this class to create instances of various types of break iterators. In particular, use getWordIterator, getLineIterator, getSentenceIterator, and getCharacterIterator to create BreakIterators that perform word, line, sentence, and character boundary analysis respectively. A single BreakIterator can 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
of
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 BreakIterator instances 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.
BreakIterator is intended for use with natural languages only. Do not use this class to tokenize a programming language.
Examples:
Creating and using text
boundaries:
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)); }
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; }(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.)
Field Summary | |
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static int |
DONE
DONE is returned by previous() and next() after all valid boundaries have been returned. |
Constructor Summary | |
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protected |
BreakIterator
() Constructor. |
Method Summary | |
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Object |
clone
() Create a copy of this iterator |
abstract int |
current
() Return character index of the text boundary that was most recently returned by next(), previous(), first(), or last() |
abstract int |
first
() Return the first boundary. |
abstract int |
following
(int offset) Return the first boundary following the specified offset. |
static Locale [] |
getAvailableLocales
() Returns an array of all locales for which the get*Instance methods of this class can return localized instances. |
static BreakIterator |
getCharacterInstance
() Returns |
static BreakIterator |
getCharacterInstance
(
Locale
Returns |
static BreakIterator |
getLineInstance
()
Returns a new BreakIterator instance for line breaks for the default locale |
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static BreakIterator |
getLineInstance
Returns a new |
static BreakIterator |
getSentenceInstance
Returns a new |
static BreakIterator |
getSentenceInstance
(
Locale
Returns a new BreakIterator instance for sentence breaks |
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abstract CharacterIterator |
getText
() Get the text being scanned |
static BreakIterator |
getWordInstance
() Returns a new |
static BreakIterator |
getWordInstance
(
Locale
Returns a new |
boolean |
isBoundary
(int offset) Return true if the specified position is a boundary position. |
abstract int |
last
() Return the last boundary. |
abstract int |
next
() Return the boundary following the current boundary. |
abstract int |
next
(int n) Return the nth boundary from the current boundary |
int |
preceding
(int offset) Return the last boundary preceding the specfied offset. |
abstract int |
previous
() Return the boundary preceding the current boundary. |
abstract void |
setText
(
CharacterIterator
newText) Set a new text for scanning. |
void |
setText
(
String
newText) Set a new text string to be scanned. |
Methods inherited from class java.lang. Object |
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equals , finalize , getClass , hashCode , notify , notifyAll , toString , wait , wait , wait |
Field Detail |
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public static final int DONE
Constructor Detail |
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protected BreakIterator()
Method Detail |
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public Object clone()
public abstract int first()
public abstract int last()
public abstract int next(int n)
public abstract int next()
public abstract int previous()
public abstract int following(int offset)
public int preceding(int offset)
public boolean isBoundary(int offset)
public abstract int current()
public abstract CharacterIterator getText()
public void setText(String newText)
public abstract void setText(CharacterIterator newText)
public static BreakIterator getWordInstance()
public static BreakIteratorgetWordInstance(Locale locale)where)
public static BreakIterator getLineInstance()
public static BreakIteratorgetLineInstance(Locale locale)where)
public static BreakIterator getCharacterInstance()
public static BreakIteratorgetCharacterInstance(Locale locale)where)
public static BreakIterator getSentenceInstance()
public static BreakIteratorgetSentenceInstance(Locale locale)where)
public static Locale[] getAvailableLocales()
protected static longgetLong(byte[] buf, int offset)
protected static intgetInt(byte[] buf, int offset)
protected static shortgetShort(byte[] buf, int offset)