Listing Files or Subdirectories

Introduction
This example illustrates how to list files and folders present in the specified directory. This topic is related to the I/O (input/output) of java.io package.
In this example we are using File class of java.io package. The File class is an abstract representation of file and directory pathnames. This class is an abstract, system-independent view of hierarchical pathnames. An abstract pathname has two components:

1. An optional system-dependent prefix string,
   such as a disk-drive specifier, "/" for the UNIX root directory, or "\\" for a Win32 UNC pathname, and
2. A sequence of zero or more string names.

Explanation
This program list the file of the specified directory. We will be declaring a function called dirlist which lists the contents present in the specified directory.
dirlist(String fname)
The function dirlist(String fname) takes directory name as parameter. The function creates a new File instance for the directory name passed as parameter
File dir = new File(fname); 
and retrieves the list of all the files and folders present in the directory by calling list() method on it. 
String[] chld = dir.list();  
Then it prints the name of files and folders present in the directory.
Code of the Program :

import java.io.*;

public class  DirListing{
  private static void dirlist(String fname){
    File dir = new File(fname);
    String[] chld = dir.list();
    if(chld == null){
      System.out.println("Specified directory does not exist or is not a directory.");
      System.exit(0);
    }else{
      for(int i = 0; i < chld.length; i++){
        String fileName = chld[i];
        System.out.println(fileName);
      }
    }
  }
  public static void main(String[] args){
    switch(args.length){
      case 0: System.out.println("Directory has not mentioned.");
          System.exit(0);
      case 1: dirlist(args[0]);
          System.exit(0);
      default : System.out.println("Multiple files are not allow.");
            System.exit(0);
    }
  }
}

Output of the Program:

C:\nisha>java DirListing example myfile.txt C:\nisha>

At the time of execution, we have specified a directory name "example" that contains only a single file "myfile.txt".
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