Regular expressions are a powerful tool for pattern matching in Java. They allow us to search for specific patterns in strings and perform operations based on those patterns. One common task is matching word boundaries in a string using regular expressions. In this blog post, we will explore how to use Java regular expressions to match word boundaries.

Word boundaries represent the positions in a string where a word starts or ends. For example, in the sentence “The quick brown fox jumps over the lazy dog,” the word boundaries can be marked as follows: The |quick |brown |fox |jumps |over |the |lazy |dog|. The vertical bars represent the word boundaries.

To match word boundaries in Java, we can use the \b anchor. The \b anchor matches at the beginning or end of a word. It represents a zero-width assertion that matches the positions where a word character is not followed or preceded by another word character. Here’s an example:

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class WordBoundaryExample {
   public static void main(String[] args) {
      String text = "The quick brown fox jumps over the lazy dog";

      Pattern pattern = Pattern.compile("\\bfox\\b");
      Matcher matcher = pattern.matcher(text);

      while (matcher.find()) {
         System.out.println("Found match at index " + matcher.start());
      }
   }
}

In the example above, we create a pattern that matches the word “fox” only if it appears on its own and not as part of another word. The \\b anchors ensure that the matched pattern is surrounded by word boundaries.

Running the above code will output:

Found match at index 16

Since “fox” appears as a separate word in the given text, it is successfully matched.

We can also use the \\b anchor to match multiple word boundaries. For example, to find all the words in a given text, we can use the following code:

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class MultipleWordBoundaryExample {
   public static void main(String[] args) {
      String text = "The quick brown fox jumps over the lazy dog";

      Pattern pattern = Pattern.compile("\\b\\w+\\b");
      Matcher matcher = pattern.matcher(text);

      while (matcher.find()) {
         System.out.println("Found match: " + matcher.group());
      }
   }
}

In this example, the pattern \\b\\w+\\b matches one or more word characters (\\w+) that are surrounded by word boundaries. Running the code will output:

Found match: The
Found match: quick
Found match: brown
Found match: fox
Found match: jumps
Found match: over
Found match: the
Found match: lazy
Found match: dog

As you can see, the code successfully matches all the words in the given text by using the \\b anchor and the \\w+ pattern.

By using the \b anchor in regular expressions, we can easily match word boundaries in Java and perform various operations. It is a useful feature when working with text manipulation and pattern matching.