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.
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.
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.
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
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));
}
Return the first boundary following the specified offset.
The value returned is always greater than the offset or
the value BreakIterator.DONE
Parameters:
offset - the offset to begin scanning. Valid values
are determined by the CharacterIterator passed to
setText(). Invalid values cause
an IllegalArgumentException to be thrown.
Create BreakIterator for word-breaks using default locale.
Returns an instance of a BreakIterator implementing word breaks.
WordBreak is usefull for word selection (ex. double click)
Create BreakIterator for word-breaks using specified locale.
Returns an instance of a BreakIterator implementing word breaks.
WordBreak is usefull for word selection (ex. double click)
Parameters:
where - the local. If a specific WordBreak is not
avaliable for the specified locale, a default WordBreak is returned.
Create BreakIterator for line-breaks using default locale.
Returns an instance of a BreakIterator implementing line breaks. Line
breaks are logically possible line breaks, actual line breaks are
usually determined based on display width.
LineBreak is useful for word wrapping text.
Create BreakIterator for line-breaks using specfied locale.
Returns an instance of a BreakIterator implementing line breaks. Line
breaks are logically possible line breaks, actual line breaks are
usually determined based on display width.
LineBreak is useful for word wrapping text.
Parameters:
where - the local. If a specific LineBreak is not
avaliable for the specified locale, a default LineBreak is returned.
Create BreakIterator for character-breaks using default locale
Returns an instance of a BreakIterator implementing character breaks.
Character breaks are boundaries of combining character sequences.
Create BreakIterator for character-breaks using specified locale
Returns an instance of a BreakIterator implementing character breaks.
Character breaks are boundaries of combining character sequences.
Parameters:
where - the local. If a specific character break is not
avaliable for the specified local, a default character break is returned.
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