The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
You invoke the getWordIterator
method to instantiate a BreakIterator
that detects word boundaries:
BreakIterator wordIterator = BreakIterator.getWordInstance(currentLocale);
You'll want to create such a BreakIterator
when your application needs to perform operations on individual words. These operations might be common word- processing functions, such as selecting, cutting, pasting, and copying. Or, your application may search for words, and it must be able to distinguish entire words from simple strings.
When a BreakIterator
analyzes word boundaries, it differentiates between words and characters that are not part of words. These characters, which include spaces, tabs, punctuation marks, and most symbols, have word boundaries on both sides.
The example that follows, which is from the program
BreakIteratorDemo
, marks the word boundaries in some text. The program creates the BreakIterator
and then calls the markBoundaries
method:
Locale currentLocale = new Locale ("en","US"); BreakIterator wordIterator = BreakIterator.getWordInstance(currentLocale); String someText = "She stopped. " + "She said, \"Hello there,\" and then went " + "on."; markBoundaries(someText, wordIterator);
The markBoundaries
method is defined in BreakIteratorDemo.java
. This method marks boundaries by printing carets (^) beneath the target string. In the code that follows, notice the while
loop where markBoundaries
scans the string by calling the next
method:
static void markBoundaries(String target, BreakIterator iterator) { StringBuffer markers = new StringBuffer(); markers.setLength(target.length() + 1); for (int k = 0; k < markers.length(); k++) { markers.setCharAt(k,' '); } iterator.setText(target); int boundary = iterator.first(); while (boundary != BreakIterator.DONE) { markers.setCharAt(boundary,'^'); boundary = iterator.next(); } System.out.println(target); System.out.println(markers); }
The output of the markBoundaries
method follows. Note where the carets (^) occur in relation to the punctuation marks and spaces:
She stopped. She said, "Hello there," and then ^ ^^ ^^ ^ ^^ ^^^^ ^^ ^^^^ ^^ ^ went on. ^ ^^ ^^
The BreakIterator
class makes it easy to select words from within text. You don't have to write your own routines to handle the punctuation rules of various languages; the BreakIterator
class does this for you.
The extractWords
method in the following example extracts and prints words for a given string. Note that this method uses Character.isLetterOrDigit
to avoid printing "words" that contain space characters.
static void extractWords(String target, BreakIterator wordIterator) { wordIterator.setText(target); int start = wordIterator.first(); int end = wordIterator.next(); while (end != BreakIterator.DONE) { String word = target.substring(start,end); if (Character.isLetterOrDigit(word.charAt(0))) { System.out.println(word); } start = end; end = wordIterator.next(); } }
The BreakIteratorDemo
program invokes extractWords
, passing it the same target string used in the previous example. The extractWords
method prints out the following list of words:
She stopped She said Hello there and then went on