Finding all words that start with an 'a' : Introduction « Regular Expressions « Java Tutorial

1. Java Tutorial
2. Regular Expressions
3. Introduction

Define the matching pattern as a word boundry, a lowercase a, any number of immedietly trailing letters numbers, or underscores, followed by a word boundary

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

public class MainClass {
  public static void main(String args[]) throws Exception {
    String candidate = "applying a pattern.";

    String regex = "\\ba\\w*\\b";
    Pattern p = Pattern.compile(regex);

    Matcher m = p.matcher(candidate);
    String val = null;

    System.out.println("INPUT: " + candidate);

    System.out.println("REGEX: " + regex + "\r\n");

    while (m.find()) {
      val = m.group();
      System.out.println("MATCH: " + val);
    }
    if (val == null) {
      System.out.println("NO MATCHES: ");
    }
  }
}