This is a basic algorithm, but it can be very useful in some situations and very handy for those that are learning Java.

The class bellow contains 4 methods:

1. the first one will list all the files and folder names under a directory
2. the second one will list all the file names under a directory
3. the third one will list all the folder names under a directory
4. the fourth one will list all the files from the directory and its sub-directories (be carefull with this one!)

Following is the code:

package com.loiane.util;

import java.io.File;

/**
 * Contains some methods to list files and folders from a directory
 *
 * @author Loiane Groner
 * http://loiane.com (Portuguese)
 * http://loianegroner.com (English)
 */
public class ListFilesUtil {

    /**
     * List all the files and folders from a directory
     * @param directoryName to be listed
     */
    public void listFilesAndFolders(String directoryName){

        File directory = new File(directoryName);

        //get all the files from a directory
        File[] fList = directory.listFiles();

        for (File file : fList){
            System.out.println(file.getName());
        }
    }

    /**
     * List all the files under a directory
     * @param directoryName to be listed
     */
    public void listFiles(String directoryName){

        File directory = new File(directoryName);

        //get all the files from a directory
        File[] fList = directory.listFiles();

        for (File file : fList){
            if (file.isFile()){
                System.out.println(file.getName());
            }
        }
    }

    /**
     * List all the folder under a directory
     * @param directoryName to be listed
     */
    public void listFolders(String directoryName){

        File directory = new File(directoryName);

        //get all the files from a directory
        File[] fList = directory.listFiles();

        for (File file : fList){
            if (file.isDirectory()){
                System.out.println(file.getName());
            }
        }
    }

    /**
     * List all files from a directory and its subdirectories
     * @param directoryName to be listed
     */
    public void listFilesAndFilesSubDirectories(String directoryName){

        File directory = new File(directoryName);

        //get all the files from a directory
        File[] fList = directory.listFiles();

        for (File file : fList){
            if (file.isFile()){
                System.out.println(file.getAbsolutePath());
            } else if (file.isDirectory()){
                listFilesAndFilesSubDirectories(file.getAbsolutePath());
            }
        }
    }

    public static void main (String[] args){

        ListFilesUtil listFilesUtil = new ListFilesUtil();

        final String directoryLinuxMac ="/Users/loiane/test";

        //Windows directory example
        final String directoryWindows ="C://test";

        listFilesUtil.listFiles(directoryLinuxMac);
    }
}