Lab Assignment #9 supplement: Classes

Due in lab, Thursday and Friday, April 15 and 16.

NOTE The in-lab exercise for this lab will not be part of lab 9 grade. However, it will count as extra credit for your assignments. We will only spend part of the lab talking about this exercise; we will discuss lab 9 and the projects during the rest of the lab.

In-Lab Work

A class hierarchy design

For this lab, you will design a somewhat conceptual class hierarchy of files and directories. A file is a superclass of different types of files. A directory is a class that has a number of files and/or directories in an array. In the lab, you will mainly use this example to come up with an object-oriented design that involves inheritance, overloading and polymorphism.

The main goal of this in-lab is to come up with a design that should satisfy some desireable properties. A proper working program is not the main goal. You probably should draw a class hierarcy diagram on paper before you actually try writing any code. You can put all your classes in the same file (remember when you put multiple classes in the same file, only one class should be public, and the rest should be defined as just classes, like the following: 

public class FileSystem {
    public static void main(String[] args) {

...
}

class File {
...
}

etc.

The above file should be saved as FileSystem.java.

Your design for this in-lab exercise should have the following properties:

  1. Lets assume you can only have two special type of files - a text file, and an image file. All other files are generic file types, for which no applications have been defined.
  2. Think about the relationship between text files, image files, and directories. Are they all types of files, or do they have a different type of relationship.
  3. All files have common properties such as name, type and size that need to be specified when a file is created. You should use the ccj Time class to set the modification time of the file to the time when the file is created.
  4. A directory can only have a fixed maximum number of files in it (say, 20).
  5. A directory can contain other directories just like it can contain other files.
  6. You can open a file with an application, or you can simply open it, in which a proper application is automatically called for known file types. For generic file types, the user is asked for what application should be called.
  7. When you open a directory all contents (both files and directories) should be displayed.
  8. You can add a file (or another directory) to a directory.
In the lab, with the help of your AI, come up with a class design that satisfies all the above properties. Draw the class hierarchy diagram, and write down all the methods and data properties that these classes should have. Then write basic skeleton structures of these methods. Your program may not do anything useful, but you should be able to compile it.