Directory operations using File class in java

/*

Directory operation 

Listing all the contents of a directory if it exists

*/

import java.io.*;

class Main

{

       public static void main(String []args)

       {

              String dirName=".";

              if(args.length==1)

                    dirName=args[0];

                   

              File d=new File(dirName);

             

              if(!d.exists())

              {

                    System.err.println("Directory Not Found - "+dirName);

                    System.exit(1);

              }

              if(!d.isDirectory())

              {

                    System.err.println("No such directory exists, "+dirName+" is a File");

                    System.exit(1);

              }

                   

              File arr[]=d.listFiles();

              for(File f:arr)

                    System.out.println(f.getName());

       }

}