Regular expressions are a powerful tool for pattern matching in Java. They allow you to search for specific patterns within strings and perform various tasks like validation, extraction, and manipulation of text. One important concept in regular expressions is the use of boundary matchers.

What are Boundary Matchers?

Boundary matchers in Java regular expressions are used to define the position of the pattern in relation to the boundaries of the input string. They do not match any specific characters, but rather indicate positions that can be used for pattern matching.

Types of Boundary Matchers

There are several types of boundary matchers available in Java regular expressions:

1. ^ - The caret (^) denotes the beginning of a line. It is used to match the pattern only if it occurs at the start of the input string.

   String regex = "^Hello";
   String input = "Hello, World!";
   System.out.println(input.matches(regex));  // Output: true
   

2. $ - The dollar sign ($) represents the end of a line. It is used to match the pattern only if it occurs at the end of the input string.

   String regex = "World!$";
   String input = "Hello, World!";
   System.out.println(input.matches(regex));  // Output: true
   

3. \b - The word boundary (\b) matches the position where a word character is not followed or preceded by another word character.

   String regex = "\\bJava\\b";
   String input = "Welcome to Java programming";
   System.out.println(input.matches(regex));  // Output: true
   

4. \B - The non-word boundary (\B) matches the position where a word character is followed or preceded by another word character.

   String regex = "\\Bprogramming\\B";
   String input = "Welcome to Java programming";
   System.out.println(input.matches(regex));  // Output: true
   

Conclusion

Boundary matchers provide a way to specify the position of a pattern in relation to the boundaries of the input string. They are useful for validating and extracting specific patterns from text. By familiarizing yourself with boundary matchers in Java regular expressions, you can enhance your pattern matching capabilities and optimize your code. #Java #RegularExpressions