Action Point Of Sale Code

package keeping;
/***
Stores static information about users: just their name and password.
Does not include the manager.
*/
import database.*;
abstract public class USR
// Please change this class from abstract to final.
{
	private static final int USER_NAME_COLUMN = 0;
	private static final int PASSWORD_COLUMN = 1;
	private DB _db = null;
 /***
 Loads the list of users from file.
 */
 USR()
 {
	 _db = new DB(Tables.USR);
  // not implemented
  // remember to delte empty user names.
  }
 /***
 Get some waitron's names.
 @return All user names which have not yet been deleted.
 */
 public String[] list() {
	int iNumOfRows = _db.length();
	String[] arrayUserNames = new String[iNumOfRows];
	String sCurrentUserName = null;
	
	for (int i = 0; i < iNumOfRows; i++) {
		 sCurrentUserName = _db.getString(USER_NAME_COLUMN, i);
		 arrayUserNames[i] = sCurrentUserName;
	 }
	
	return arrayUserNames;
 }
 /***
 Delte the specified user.
 @param index Which user to delete. >= 0
 */
 abstract void delete(int index) ; // Just set user name to "", then call db.delete().
 /***
 Adds a newly created user to the database.
 @param userName This may contain spaces.
 @param password String of digits.
 @throws IllegalArgumentException if the password does not match the criteria specified in {@link change
 }
Or if the  userName parameter is empty.
*/
public void add(String userName, String password) {
	if (isPasswordValid(password)) {
		_db.add(new String[] {userName, password});
	} else {
		throw new IllegalArgumentException();
	}
}

/***
 * Checks if a given password is valid according to the change method logic.
 * @param sPassword
 * @return
 */
private boolean isPasswordValid(String sPassword) {
	if (isStringLength3(sPassword) && isStringNumeric(sPassword)
			&& !isPasswordInUse(sPassword)) {
		return true;
	} else {
		return false;
	}
}

/***
 * Checks if a string's length equals 3.
 * @param string
 * @return
 */
private boolean isStringLength3(String string) {
	if (string.length() == 3) {
		return true;
	} else {
		return false;
	}
}

/***
 * Checks if a given password already exists in the DB.
 * @param sPassword
 * @return
 */
private boolean isPasswordInUse(String sPassword) {
	String sCurrentPassword = null;
	int iNumOfRows = _db.length();
	
	for (int iCurrentRow = 0; iCurrentRow < iNumOfRows; iCurrentRow++) {
		sCurrentPassword = _db.getString(PASSWORD_COLUMN, iCurrentRow);
		if (sCurrentPassword.equals(sPassword)) {
			return true;
		}
	}
	
	return false;
}

/***
 * Checks if a given string's characters are all numbers.
 * @param string
 * @return
 */
private boolean isStringNumeric(String string) {
	try {
		Integer.parseInt(string);
	} catch (NumberFormatException numberFormatException) {
		return false;
	}
	
	return true;
}

/***
Create a random password.
@return Some characters.
*/
static String generate()
{
 return "123";
 }
/***
Change  password.
@param index the position of the user in the list() array.
@param newPassword Must comply with rules below:
@throws IllegalArgumentException If newPassword is not three characters long, or if it does not consist entirely of digits, or if it is in use by another user!
*/
public void change(int index, String newPassword) {
	if (isPasswordValid(newPassword)) {
		_db.setString(PASSWORD_COLUMN, index, newPassword);
	} else {
		throw new IllegalArgumentException();
	}
}
/***
Have a quick look at a user's current password.
<p>
Naughty, naughty!
@param index User offset.
@return The user's password.
*/
public String peek(int index) {
	return _db.getString(PASSWORD_COLUMN, index);
}

}