下列程序用于显示指定目录下的子目录及文件名，请填写所缺少的代码；import java.io.*;public class test{public static void main(String[] args){String s1,s2[];try {InputStreamReader in=new InputStreamReader(System.in);BufferedReader bin=new BufferedReader(in);System.out.println("please input a File name:");s1=________________________________;File f=new File(s1);System.out.println(f.isDirectory());if(_________________){//判读是否为目录int n=(f.list()).length;s2=new String[n];s2=____________;//获取子目录及文件名for(int i=0;i