For this programming assignment you will write a recursive algorithm to display the contents of a directory in a computers file system. You will also get a little experience using the API documentation for several components of the JDK library, including the File class. Additionally, you will get some exposure to a graphical user interface (GUI), which you may or may not have had in your previous Java work.

The Explorer program that serves as the default file system browser for the Windows XP operating system allows you to see the first-level contents of a given folder. It does not allow you to see the contents of any nested subfolders you have to click on each subfolder, one at a time, to see the contents of these folders. Suppose you wanted to see the entire contents of a given folder; i.e., not just the first-level files and subfolders, but everything that is contained in all the nested subfolders, regardless of how many nested subfolders there are.

You could write an algorithm that iterates through all the subfolders using a loop, but since you have know way of knowing beforehand how many levels of nested subfolders there are, implementing an iterative algorithm to do this would be tricky. This problem is perfectly suited for a recursive algorithm, however. Each subfolder constitutes a problem that is similar to the initial problem (i.e., the root-level folder), only smaller. Recursion can theoretically (though not practically) handle an infinite amount of nesting.

Your goal for this assignment is to implement a recursive method that will enumerate the contents of a chosen folder in a computers file system, and display the following information about all the files and subfolders in the chosen folder:

1. absolutepathname(i.e.,thepathnamebeginningwiththedriveletterornetwork share; e.g.: C:\My Documents\myFile.txt)

2. size, in kilobytes

3. type (file or folder)

4. the date and time on which the file or folder was last modified

Provided Template Files

I am providing a set of template files for you to modify to complete this assignment. These files are contained in the DirectoryLister.zip archive that you can download from the Canvas site in Module 2. There are 3 files you will need to use for this assignment:

1. Driver.java 2. GUI.java 3. DirectoryLister.java

The only file you will need to modify for this assignment will be DirectoryLister.java. You will not need to create any additional classes for this assignment. You should be able to compile the project as it is. It will allow you to select a directory, but it wont do anything else.

How the Program Should Work

A screen capture of how the user interface appears when the program is first launched is shown below. This is what you should see if you compile and run the provided source files as they are, with no modifications. Clicking the Browse... button will bring up a JFileChooser dialog where you can select a folder from the file system. Once you have selected a folder, a table will be generated showing the name, size, type, and date last modified for every file and folder in the selected folder, as well as all nested subfolders. With the files you download in the directoryLister.zip file, selecting a folder will do nothing. You must complete the implementation to process the selected folder and display all the required information.

What you need to do

All you need to do for this assignment is complete the following 2 methods of the DirectoryLister class. The method declarations have been provided for you. All you need to do is provide the implementations. You will need to understand how the GUI works, though in order to get your results to display properly.

/** Show the directory listing.

• * An error message is displayed if basePath does not represent a

• * valid directory. *

• * @param basePath * */

  public void showDirectoryContents(String basePath)

  { // TODO

  }

/** Recursive method to enumerate the contents of a directory. *

* @param f directory to enumerate

*/ private void enumerateDirectory(File f)

{ // TODO

}

The value returned by the JFileChooser dialog is a string representing the absolute path of the selected folder. There are a few exceptional situations you should try to make sure are handled by validating the input returned from the JFileChooser dialog:

1. If the user clicks the Cancel button or the Close button on the JFileChooser dialog, without choosing a folder.

2. IftheuserentersaninvalidfolderpathdirectlyintothetextboxontheJFileChooser dialog, or modifies a path selected by clicking on a folder in the dialogs file/folder view.

3. It is possible, albeit , for a chosen folder to exist at the time of choosing it in the JFileChooser dialog, but not exist after the user clicks the Open button on the dialog. An example of how this could happen would be a concurrently running process that happens to delete or rename the chosen folder in between the time the folder was chosen, and the Open button is clicked.

You may find that setting up a try-catch block to handle these situations is helpful. In any event, the program should not exit or crash when one of these situations occurs, but it should behave appropriately; e.g., by displaying a message using a JOptionPane dialog to inform the user what has occurred.

If the chosen directory is valid, the enumerateDirectory method should be called, which should recursively enumerate the contents of the chosen folder. To get full credit for this part of the assignment, your enumerateDirectory method must be recursive, and it should update the display with all the required information. You can use the updateListing method of the GUI class to do this. The arguments for this method are 4 references to String objects

the absolute path of a directory in the file system.

that represent the absolute path, size, type (folder or file), and the date last modified for the file or folder currently being processed.

Relevant Classes in the Java API

File JOptionPane

The File class is an abstract representation of either a file or a folder in the file system. To create a File object, you will probably want to use the constructor, File (String pathname), since this is the type of information returned when the initial folder is chosen from the JFileChooser dialog. The File class provides many useful methods, including ones to retrieve all the information you need to display for each file or folder. I will leave it to you to read through the API docs to figure out which methods you need.

The JOptionPane class is used to display a simple modal dialog box containing a message. It can also display things like warning icons to indicate the seriousness of the message. You dont need to create an instance of the JOptionPane class in order to use it. You can use one of the many static methods the JOptionPane class provides. For example, the following statement will display an error message that reads, The specified filename is invalid!:

JOptionPane.showMessageDialog(null, The specified filename is invalid! , Error, JOptionPane.ERROR_MESSAGE);

The first argument here refers to the parent component of the JOptionPane. Since were calling one of the static methods, we dont need to specify a parent component, so we pass a null value. The second argument is the error text that will be displayed in the main part of the message dialog. The third argument specifies the text that should appear in the title bar of the dialog. Finally, the fourth argument specifies which type of icon should be displayed along with the error message (warning, information, or error).

Hints

1. Dontmakethisprojectharderthanitreallyis!Ivegivenyou2weekstofinishit,butyou dont really have to do that much workyou only need to implement the two methods Ive indicated.

2. You should not need to create any additional methods or classes. The user interface is built for you, so you do not have to create any additional UI components. You will need to understand how the user interface works, though, so you can make your implementation communicate with it.

3. Your showDirectoryContents method needs to call your enumerateDirectory method, which requires a File object as a parameter, so at some point you will need to create a File object in your showDirectoryContents method.

4. YourenumerateDirectorymethodmustberecursive,soyouwillneedtodeterminewhatthe base case(s) are, and what the recursive case(s) are. If you think about how a computers file system is structured, you should be able to figure this out pretty quickly.

5. Test your program before you submit it! Make sure your test cases cover all the possible scenarios:

1. a non-existent folder (you can do this by typing an invalid path in the text box of the interface, instead of choosing an existing directory)

2. an empty folder

3. a folder containing only one file

4. a folder containing only one subfolder

5. a folder containing multiple files (but no subfolders)

6. a folder containing multiple, non-nested subfolders (but no files)

7. a folder containing both files and subfolders (all folders are non-nested)

8. a folder containing multiple, nested subfolders (but no files)

9. a folder containing an arbitrary mix of files and subfolders (some nested, some non-nested)

6. Dontworryaboutexhaustivelytestingyourprogramonafoldercontaingahugenumber of files and subfolders. While recursion is elegant, it can quickly eat up all the stack space in your computers memory, and if this happens the program will crash. Test your program on folders with moderate numbers of files and subfolders, and assume that if your program works on those folders, it will work for all folders.