listFiles(),如何实现FileFilter及其FilenameFilter接口，list()的使用

1. import java.io.*;
   //Oniy类实现了FileFilter接口
   class OnlyExt implements FilenameFilter{
   	String ext;
   	public OnlyExt(String ext){
   		this.ext="."+ext;
   	}
   	public boolean accept(File dir,String name){
   		return name.endsWith(ext);
   	}
   }
   class FileFilterTest implements FileFilter{
   	String filename;
   	FileFilterTest(String filename){
   		this.filename=filename;
   	}
   	public boolean accept(File name){
   		if(name.getName().lastIndexOf(filename)!=-1)
   			return true;
   		else return false;
   	}
   	
   }
    class DirListOnly {
   	  static void p(File[] f){
   		 for(File x:f)
   			 System.out.println(x);
   		 System.out.println();
   	 }
   public static void main(String[] args){
   	String dirname="c:/";
   	File f1=new File(dirname);
   	FilenameFilter only=new OnlyExt("txt");
   	String s[]=f1.list(only);
   	
   	for(int i=0;i<s.length;i++)
   		System.out.println(s[i]);
   	System.out.println("\n");
   	File[] f2=f1.listFiles();
   	File[] f3=f1.listFiles(only);
   	File[] f4=f1.listFiles(new FileFilterTest("txt"));
   	
   	p(f2); 
   	p(f3);
   	p(f4);
   }
   }