Java正则表达式：什么是非捕获组

// 演示非捕获组概念

import  java.util.regex. * ;
public   class  NonCapture
... {
      
      public static void main(String[] args)
      ...{
      
              String inputStr = "abbabcd";
             String patternStr = "(a(?:b*))+(c*)";
            //String patternStr = "(a(b*))+(c*)";   
            //String patternStr = "(a)+(c*)";
            // (?:b*) is a non-capturing group
            
            // Compile and use regular expression
            Pattern pattern = Pattern.compile(patternStr);
            Matcher matcher = pattern.matcher(inputStr);
            boolean matchFound = matcher.find();
            
            if (matchFound) 
            ...{
                // Get all groups for this match
                for (int i=0; i<=matcher.groupCount(); i++)
                ...{
                    String groupStr = matcher.group(i);
                    System.out.println("group"+i+" "+groupStr);
                }
                // group 0: abbabc
                // group 1: ab
                // group 2: c
            }
            
            System.out.println("groupCount()="+matcher.groupCount());

    }
    
}

 

输出结果如下图。充足可以看到，非捕获组没有计算在 groupCount()在内