java 使用正则表达式

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

public class FindA{  
  public static void main(String args[])  
  throws Exception{  
 
    String candidate =  
     "A Matcher examines the results of 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: ");  
    }  
  }  
}