CMSC 131: Homework 6 - Accounts Management System

Homework #6	CMSC 131
Due Friday July 23^rd, 2004	Object-Oriented Programming I
Type of Homework: Closed	Summer 2004

Objective

This homework will give you practice with one-dimensional arrays of references, class design, and class implementation.

Overview

Management of computer accounts is one of the the tasks computer system administrators are responsible for. Typical activities include: account creation/removal, quota increase, and information reports. In this homework you will implement a simplified version of an account manager.

For this homework, support classes will not be provided. The only files available in the code distribution are a Driver.java file which just starts the system you will implement, and a timelog file. You will design and implement all the classes of the system.

This homework will be graded as follows:

80% - Implementation
10% - Javadoc documentation
10% - Time log

Specifications

Terms

Before we continue, let's define some terms we will be using throughout the description.

User Name - Refers to the person a computer account has been assigned to. It may include first name, last name, and middle initial. For simplicity we will assume names are unique (i.e., two people will not have the same name).
Login Name - Refers to the collection of characters that identifies an account. For example, my WAM account has has login name "nelsonp". Login names will be unique (i.e., no two accounts will have the same login name).
Quota - Fraction of the disk space that belongs to an account.
Disk Space - Amount of disk space a computer has.
Disk Usage - Amount of disk space being used for accounts.

We will use megabytes (MB) as the disk space unit.

Tasks

You will write a program that enables a system administrator complete the following tasks:

Create a computer account for a user.
Remove (delete) a computer account.
Increase the quota of an account.
Display information about an account.
Display information about all accounts in the system.

For simplicity our system only have one computer. When the program starts, it prompts the system administrator for the name of the computer and the maximum disk space. Afterwards the program will process the aforementioned tasks until the "quit" option is chosen. The "Sample Run" section provides a sample run of the program you are expected to write.

Your Assignment

You assignment consists in implementing three classes that will represent the accounts management system. The classes are:

Account - represents a computer account. It has (at least) the String reference fields userName, loginName, and password. In addition, it has a double field name quota.
Computer - represents a computer. It has the following fields:
- name - String reference representing the name of the computer.
- maxDiskCapacity - double field representing the maximum disk capacity of the computer.
- diskUsage - double field representing the disk usage.
- accounts - one-dimensional array of references to Account objects.
AccountsManager - represents the manager of the system and where execution will start.

You can other fields (instance variables) if you understand they are necessary.

Methods to Implement

The description below provides an idea of some of the methods each of the classes must have. By no means the list is complete. It is your responsibility to define any necessary methods so that you can implement the account management system.

Account
- constructor - This method takes as parameters a user name, a login name, a password and a quota value. It initializes the object fields accordingly.
- toString - This method generates a String with the following format:
"UserName: <userName>, LoginName: <loginName>, Password: <password>, Quota: <quota>" where <userName>,<loginName>,<password> and <quota> represent the field values associated with the account. See the Sample output to get an idea of the format to follow.
get/set methods - Any get/set methods you understand are necessary.

AccountsManager
- runManager - You must implement this method. This is the method that starts the computer account manager. Through this method you will display the set of computer account management choices and process user requests. This is the method called by the driver we have provided. In this method, you will create a Computer object that will be used to process computer account tasks.
- other methods - Feel free to add any other method you understand are necessary.
Computer
- constructor - Initializes a computer with a particular name and maximum disk capacity.
- createAccount - This method will create a computer account and it will place it in the array of computer accounts. The accounts must be placed in the array so that the accounts are sorted in increasing ordered by login name. This is a very important requirement you must satisfy. Creating an account will be possible if there is enough disk space to satisfy the quota requirements for the account and if the requested login name is not already in use. Otherwise the creation of the account will fail. The computer diskUsage should be adjusted accordingly.
- removeAccount - This method will remove a computer account. The method requires the login name of the account to remove. The operation will be successful if there is an account that corresponds to that login name. The diskUsage of the computer should be adjusted accordingly.
- increaseQuota - This method will increase the quota of an existing account by a particular value. For example, if the account has a quota of 5 MB, then we can increase the quota to 6 MB by calling the method with a value of 1 MB. The method takes as parameters the account login name and the quota increase value.
- toString - This method generates a String with the following format:

"Computer Name: "<computerName>

"DiskUsage: " <diskUsage>

"MaxDiskCapacity: "<maxDiskCapacity>

"Accounts:"

where <computerName>, <diskUsage>, <maxDiskCapacity> and <listOfAccounts> represent the field

values associated with the computer.

You should implement the classes in the following order: Account, Computer and finally AccountsManager.

Error Conditions

Each task have a set of possible errors that could occur. Your program is expected to detect and in some cases report the errors. The description that follows specifies the errors you are expected to report. Error messages should be generated using JOptionPane.showMessageDialog. After printing the error message, the current task will end and the task menu should be displayed to process the next user request.

create account task -
- User is trying to create an account with a login name already is used. Your program must display the message "ERROR: Login already in use".
- User is trying to create an account with a quota value that exceeds the available disk space. For this error your program must display the message "ERROR: Not enough disk space".
- If the user has provided both an invalid login name and an invalid quota amount display only the error associated with invalid login name.
remove account task -
- User is trying to remove an account with an invalid login name. Your program must display the message ""ERROR: Account does not exist".
increase quota task
- User is trying to increase quota by an invalid value. Your program must display the message "ERROR: Not enough disk space."

You can assume that for other tasks and scenarios not covered by the above error conditions the user is providing the expected data and in the correct format.

Requirements

You must use meaningful variable names and good indentation.
You may not use the ArrayList class.
Your arrays must have the minimum size possible at all times.
You must avoid code duplication.
You must implement and use the classes Account, Computer, and AccountManager.
Computer accounts must be kept ordered by login name.
The Computer class must declare and use an array of references to Account objects.
You must provide javadoc comments for class methods.
You can define additional classes if you understand is necessary.

Sample Run

Keep in mind this is just an sample run. Your code must work for other scenarios.

Starting the system and providing a computer name