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Word Boundaries

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

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