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]);
    }
 }
}