FilenameFilter接口中，accept 方法回调问题

见下面的程序，这个回调是怎么发生的啊？从程序中怎么看不出逻辑，都没有调用accept()？

public class DirList
{
        public static void main (String [ ] args)
        {
                File path = new File (".") ; 
                String[ ] list ;
                if ( args . length == 0 )
                {
                        list = path . list ( ) ;
                }
                else 
                {
                        list = path . list (new DirFilter ( args [ 0 ])) ; 
                }
                Arrays . sort (list , String . CASE_INSENSITIVE_ORDER );
                for (String dirItem : list ) 
                    System . out . println (dirItem) ;        
        }
}
class DirFilter implements FilenameFilter 
{
        private Pattern pattern ; 
        public DirFilter ( String regex )
        {
                pattern = pattern . compile ( regex );
        }
        
        public boolean accept ( File dir , String name )
        {
                return pattern . matcher ( name ) . matches (  ) ;
        }
}