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Java™ Platform Standard Ed. 6 |
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java.lang.Object extended by java.text.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 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.
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 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.)
CharacterIterator
| Field Summary | |
|---|---|
static 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. |
| Constructor Summary | |
|---|---|
protected |
BreakIterator()
Constructor. |
| Method Summary | |
|---|---|
Object |
clone()
Create a copy of this iterator |
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). |
abstract int |
first()
Returns the first boundary. |
abstract int |
following(int offset)
Returns the first boundary following the specified character 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 a new BreakIterator instance
for character breaks
for the default locale. |
static BreakIterator |
getCharacterInstance(Locale locale)
Returns a new BreakIterator instance
for character breaks
for the given locale. |
static BreakIterator |
getLineInstance()
Returns a new BreakIterator instance
for line breaks
for the default locale. |
static BreakIterator |
getLineInstance(Locale locale)
Returns a new BreakIterator instance
for line breaks
for the given locale. |
static BreakIterator |
getSentenceInstance()
Returns a new BreakIterator instance
for sentence breaks
for the default locale. |
static BreakIterator |
getSentenceInstance(Locale locale)
Returns a new BreakIterator instance
for sentence breaks
for the given locale. |
abstract CharacterIterator |
getText()
Get the text being scanned |
static BreakIterator |
getWordInstance()
Returns a new BreakIterator instance
for word breaks
for the default locale. |
static BreakIterator |
getWordInstance(Locale locale)
Returns a new BreakIterator instance
for word breaks
for the given locale. |
boolean |
isBoundary(int offset)
Returns true if the specified character offset is a text boundary. |
abstract int |
last()
Returns the last boundary. |
abstract int |
next()
Returns the boundary following the current boundary. |
abstract int |
next(int n)
Returns the nth boundary from the current boundary. |
int |
preceding(int offset)
Returns the last boundary preceding the specified character offset. |
abstract int |
previous()
Returns 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 |
|---|
equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
| Field Detail |
|---|
public static final int DONE
| Constructor Detail |
|---|
protected BreakIterator()
| Method Detail |
|---|
public Object clone()
Cloneablepublic abstract int first()
public abstract int last()
public abstract int next(int n)
BreakIterator.DONE and 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 return
BreakIterator.DONE and the last text boundary would become the
new text position.
n - which boundary to return. A value of 0
does nothing. Negative values move to previous boundaries
and positive values move to later boundaries.
BreakIterator.DONE if either first or last text boundary
has been reached.public abstract int next()
BreakIterator.DONE and
the iterator's current position is unchanged. Otherwise, the iterator's
current position is set to the boundary following the current boundary.
BreakIterator.DONE if the current boundary is the last text
boundary.
Equivalent to next(1).next(int)public abstract int previous()
BreakIterator.DONE and
the iterator's current position is unchanged. Otherwise, the iterator's
current position is set to the boundary preceding the current boundary.
BreakIterator.DONE if the current boundary is the first text
boundary.public abstract int following(int offset)
BreakIterator.DONE and 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 value
BreakIterator.DONE.
offset - the character offset to begin scanning.
BreakIterator.DONE if the last text boundary is passed in
as the offset.
IllegalArgumentException - if the specified offset is less than
the first text boundary or greater than the last text boundary.public int preceding(int offset)
BreakIterator.DONE and 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 value
BreakIterator.DONE.
offset - the characater offset to begin scanning.
BreakIterator.DONE if the first text boundary is passed in
as the offset.
IllegalArgumentException - if the specified offset is less than
the first text boundary or greater than the last text boundary.public boolean isBoundary(int offset)
offset - the character offset to check.
true if "offset" is a boundary position,
false otherwise.public abstract int current()
BreakIterator.DONE because either first or last text boundary
has been reached, it returns the first or last text boundary depending on
which one is reached.
next(),
next(int),
previous(),
first(),
last(),
following(int),
preceding(int)public abstract CharacterIterator getText()
public void setText(String newText)
newText - new text to scan.public abstract void setText(CharacterIterator newText)
newText - new text to scan.public static BreakIterator getWordInstance()
BreakIterator instance
for word breaks
for the default locale.
public static BreakIterator getWordInstance(Locale locale)
BreakIterator instance
for word breaks
for the given locale.
locale - the desired locale
NullPointerException - if locale is nullpublic static BreakIterator getLineInstance()
BreakIterator instance
for line breaks
for the default locale.
public static BreakIterator getLineInstance(Locale locale)
BreakIterator instance
for line breaks
for the given locale.
locale - the desired locale
NullPointerException - if locale is nullpublic static BreakIterator getCharacterInstance()
BreakIterator instance
for character breaks
for the default locale.
public static BreakIterator getCharacterInstance(Locale locale)
BreakIterator instance
for character breaks
for the given locale.
locale - the desired locale
NullPointerException - if locale is nullpublic static BreakIterator getSentenceInstance()
BreakIterator instance
for sentence breaks
for the default locale.
public static BreakIterator getSentenceInstance(Locale locale)
BreakIterator instance
for sentence breaks
for the given locale.
locale - the desired locale
NullPointerException - if locale is nullpublic static Locale[] getAvailableLocales()
get*Instance methods of this class can return
localized instances.
The returned array represents the union of locales supported by the Java
runtime and by installed
BreakIteratorProvider implementations.
It must contain at least a Locale
instance equal to Locale.US.
BreakIterator instances are available.
|
Java™ Platform Standard Ed. 6 |
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