CS 1723/1721 Data Structures Laboratory 9

CS 1721 Laboratory 9
Using recursion to traverse a directory

Objectives:

Practice with recursion.
Learn about directory structure on computer systems.
Learn to work with file objects and properties.
Introduce the idea of tree organization.

Hand-in Requirements;

Source for DirectoryList.java (10 pts)
Source for DirectoryListTest.java (5 pts)
Source for FileTest (5 pts)

All projects and laboratories will be submitted electronically through webCT. Zip up your entire project directory to submit as the source. (Right click on the project folder and follow the SentTo link.) There is no output required for this lab as the grader will test the running of your code. Please organize your output neatly so that it is readable and identified with its part in the lab.

Overview:

This recitation exercise explores how to access system directories through the File class that is part of the java.io package. Directories under the Windows and Unix operating systems have a tree structure. That is, a directory is just a file that contain files and other directories. The files and other directories are its children and it is the parent. Showing all of the files in a directory tree (showDirectoryTree) is naturally a recursive process:

Output this file's name and information.
If this file is not a directory, return (the base case).
For each child file, call showDirectoryTree (the recursion step).

The project will use the Java File class ( http://java.sun.com/j2se/1.5/docs/api/java/io/File.html) that is part of the java.io package.

Part I: Project setup and experimentation with `File` objects.

Create a new Jbuilder project called directories. Add a FileTester class that has a main method but no constructor. Add a line to the main method that outputs: "CS 1723 Laboratory 9 Part I: Written by YOURNAME". Compile and run.

Add the following code to FileTester and run the program for several test files.

Prompt the user to enter a string representing a filename.
Use the Scanner class to read in the filename entered by the user.
Create a File object corresponding to the filename that was entered. (Note: a File object does not necessarily have a real file on disk.)
Output the name and full path of the File object.
Output whether the File object can be read or written to.
Output the length and the time the File object was last modified. (Hint: you can use a Date object to convert a long time since the Epoch to a readable date.)

Now add code to test whether the File object is a directory. If the File object is a directory, get a list of the names of the files that the directory contains. Output the file names in the directory one per line indented from the directory name.

On your own, put the code in a loop so that you can add several files. Experiment with different files and with giving just file names and with giving full path names.

Part II: Directory traversal and display

Create a DirectoryList class with no main method and a DirectoryListTest class with a main method. Add a statement to the main method of DirectoryListTest to output CS 1723 Laboratory 9 Part II and III: Written by YOURNAME". Compile and run.

Implement a static method in DirectoryList called showDirectory:
```
   public static showDirectory(String filename)
```
That recursively displays the directory tree corresponding to filename using the recursive algorithm outlined in the overview.

Add test code to the main method of DirectoryListTest to use showDirectory to output several different directory trees.

Note: The array of strings returned by the list method of File just gives filenames. You need to concatenate that file name to the directory path name in order to get the right file when you proceed with the recursive calls.

Part III: Enhancing the directory display (on your own)