Go4Expert - how FilenameFilter works?

With reference to the code below can u tell me when and how accept() method of FilenameFilter is called,and from where parameter of accept() method are passed?
In a nutshell i mean to say how FilenameFilter works?

Code:

import java.io.*;



pubic class OnlyExt implements FilenameFilter

{

  String str;

 

   public OnlyExt(String str)

   {

        this.str="."+str;

    }



 public boolean accept(File dir,String name)

   {

       return name.endsWith(str);

   }

}



class DirListOnly

{

   public static void main(String [] args)

   {

      String dirname="/java";

       File f1=new File(dirname);

       FilenameFilter only=new OnlyExt("html");

       String s[]=f1.list(only);



    for(int i=0;i<s.length;i++)

    {

       System.out.println(s[i]);

    }

 }

}