Overview

960679#Darwin, Charles#Biology
8008765#Wareham, Todd#Computer Science
008765#Schweitzer, Albert#Medicine
160011#Einstein, Albert#Physics

This file has 4 entries and 3 fields per entry; field 2 of entry 3 is "Schweitzer, Albert" and field 3 if entry 4 is "Physics". Such database files are known as flat files.

In this assignment, you will implement both a generic flat file class and a class that uses this generic class to implement a password database.

Specification

• FlatFile: This class implements a generic database file and its operations. This class will have the following publicly-accessible methods:
  public FlatFile(String filename, String fieldSep, int numFields)
  
  throws IOException, FileFoundException, FileNotFoundException, BadFlatFileException
  
  Establishes a new flatfile-object based on the system file named filename such that fields are separated within entries by the characters in string fieldSep and each line has exactly numFields fields. Throws exception FileNotFoundException with appropriate exception-message if flatfile not found, not readable, or not writable, throws exception FileFoundException with appropriate exception-message if the temporary flatfile associated with that flatfile is found (see below), and throws exception BadFlatFileException if any line in the specified flatfile does not have the specified number of fields.
  public int numEntries() throws IOException
  
  Returns the number of entries in the flatfile.
  public boolean hasEntry(String entry) throws IOException
  
  Returns true if string entry is an entry in the flatfile, and false otherwise.
  public boolean addEntry(String entry)
  throws IOException, BadFlatFileEntryException
  
  Attempts to add string entry as an entry to the flatfile. Returns false if the entry already exists in the flatfile and true otherwise. Throws exception BadFlatFileEntryException if the given entry does not have the required number of fields for the flatfile.
  public boolean replaceEntry(String oldEntry, String newEntry)
  throws IOException, BadFlatFileEntryException
  
  Attempts to replace entry oldEntry in the flatfile with entry newEntry. Returns false if oldEntry is not in the flatfile and true otherwise. Throws exception BadFlatFileEntryException if newEntry does not have the required number of fields for the flatfile.
  public int numTaggedEntries(int field, String tag)
  throws IOException, BadFlatFileFieldException
  
  Returns the number of entries in the flatfile that have field-value tag in field number field. Throws exception BadFlatFileFieldException if the requested field-number is not valid for the flatfile.
  public String[] getTaggedEntries(int field, String tag)
  throws IOException, BadFlatFileFieldException
  
  Returns all entries in the flatfile that have field-value tag in field number field. If there are no such entries, returns null. Throws exception BadFlatFileFieldException if the requested field-number is not valid for the flatfile.
  public String[] getText() throws IOException
  
  Returns all entries in the flatfile. If there are no entries, returns null.
  public void saveText(String[] text) throws IOException
  
  Replaces the contents of the given flatfile with the entries in text.

  These methods should be the only publicly-accessible elements in this class. Note that all of these methods throw exception IOException to account for basic I/O errors not dealt with by this class, e.g., file permissions changing in mid-execution. Where necessary, various methods can use a temporary flatfile called filename.temp; however, if such a file is created in a method, it must be destroyed by the time that method terminates. This class must be the only class-definition contained in file FlatFile.java.

• PasswordDb: This class implements a password database using FlatFile. Each line in such a file will consist of two fields separated by a hash ('#') character, a login-name and a password. Names and passwords are unique, i.e., each password has exactly one associated name and each name has exactly one associated password. This class will have the following publicly-accessible methods:
  public PasswordDb(String filename)
  throws IOException, FileFoundException, FileNotFoundException, BadFlatFileException
  
  Establishes a new password database based on the flatfile named filename. Throws all exceptions issued by the FlatFile constructor.
  public boolean load() throws IOException
  
  Loads associated flatfile contents into password database for faster access and manipulation. If the database has already been loaded, aborts loading and returns false; otherwise, performs loading and returns true.
  Note that once loading has occurred, all methods in this class use this loaded information until this information is saved back to the file using method save (see below), at which time all methods revert to operating on the file.
  public boolean isLoaded()
  
  Returns true if the password database has been loaded and false otherwise.
  public boolean numEntries() throws IOException
  
  Returns the number of entries in the password database.
  public boolean nameExists(String name) throws IOException
  
  Returns true if there is already a password-entry for the given name name and false otherwise.
  public boolean passwordExists(String password) throws IOException
  
  Returns true if there is already a password-entry with the given password password and false otherwise.
  public boolean entryExists(String name, String password) throws IOException
  
  Returns true if the specified password entry exists and false otherwise.
  public boolean addEntry(String name, String password) throws IOException
  
  Attempts to add the specified password entry to the password database. If both the name and the password do not already exist in the database, the entry is added and returns true; otherwise, aborts add and returns false.
  public boolean changePassword(String name, String oldPassword, String newPassword) throws IOException
  
  Attempts to change the password of the specified entry in the password database. If the specified entry does not already exist in the database, the change is made and returns true; otherwise, aborts add and returns false.
  public boolean save() throws IOException
  
  Replaces information in password file with that in the password database object. If password database object has has not already been loaded, aborts save and returns false; otherwise, performs save and returns true.

  These methods should be the only publicly-accessible elements in this class. Note that all of these methods throw exception IOException to account for basic I/O errors not dealt with by this class, e.g., file permissions changing in mid-execution. Note also that where necessary, certain exceptions thrown by flatfile methods are "absorbed" and not thrown by the methods above. This class must be the only class-definition contained in file PasswordDb.java.

• FlatFile.java (skeleton)
• FileFoundException.java
• BadFlatFileException.java
• BadFlatFileFieldException.java
• BadFlatFileEntryException.java

Fill in missing details and fully comment the code in FlatFile.java; places where you need to fill in code are denoted by the inline comment "*** PERFORM MAGIC HERE ***". All other given Java files are complete as they are. You will have to write your own file containing the class-definition of PasswordDb as described above.

IMPORTANT: As your submitted code will be tested using programs that assume the classes and methods described above, the classes in your submitted code must be named and all methods in these classes must be defined EXACTLY as specified above. Submitted code not conforming to these specifications will not be tested and marks will be deducted accordingly.

Hints

Adding a line to a file is much easier if writing is done using the append version of the constructor for the FileWriter class.

Various methods in class File, e.g., renameTo, delete, are very handy not only for querying files existence or permissions but also for performing LINUX shell operations on files like renaming or deletion.

Each PasswordDb object will should have an associated flatfile object.

Remembering whether or not a PasswordDb object has been loaded or not can be done very easily using a private boolean variable loaded; such a variable should be initialized to false when the object is created, its value modified accordingly by methods load and save, and its value checked by all other methods as necessary.

You may use any data structures you wish to implement the storage for the password database inside a PasswordDb object. May I suggest using a pair of vectors to store the passwords and names, respectively.

Compiling and Running

See appropriate web pages for instructions on compiling and running Java programs.

Submitting Your Programs

Please submit your program files FlatFile.java and PasswordDb.java using system program submit-assignment by the due date. No hardcopies of these files need to be passed in to me. NOTE: If you are using non-standard classes for input or output, e.g., Keyboard, EasyReader, please submit files containing theses class definitions along with the requested Java files.

Additional Notes:

• Oct 11, 8:30am
  Assignment #2 posted.

Created: October 10, 2000
Last Modified: October 13, 2000