CS367 Programming Assignment 2
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OverviewWhy are we doing this program? DescriptionYou probably have seen an LED display that loops through a sequence of messages (such as is depicted here). For this assignment you will implement a simple console-based editor that allows a user to create, edit, save, and load sequences of messages (which could then be uploaded into an LED-type display and shown in a continuous loop). It is typical for today's programmers to use ADTs that are already implemented as part of a class library (e.g., C++ Standard Template Library) or an API (e.g., Java's Application Program Interface). Understanding ADT implementations is still important to be able to make informed choices as to which ADT implementation is best suited for an application in terms of memory and time efficiencies. For example, knowing the tradeoffs between array and linked implementations of the List ADT helps us choose between Java's ArrayList and LinkedList classes. It is also important to be able to implement your own data structures when pre-built ones are not available or when standard ADTs (and their operations) are unsuitable for the intended application. In this assignment we provide you with an interface for a specialized ADT called a Loop. In addition to the main message loop editor application class, you will write a class which implements a Loop ADT using a circular doubly-linked list, as well as iterator and exception classes needed to support your Loop ADT implementation. GoalsThe goals of this assignment are to:
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SpecificationsWhat are the program requirements? The Loop ADTA Loop is essentially a circular List. However, unlike a List, a Loop does not have a beginning or an end and items within the Loop cannot be accessed using a position. Instead, the Loop has a current item and the ability to move forward or backward. A Loop can be modified by removing the current item or by inserting an item before the current item. The Loop ADT is represented in Java by the Loop<E> interface which is provided for you (see Loop.java). Complete information about Loop operations can be found in the javadoc for the Loop<E> interface. The LinkedLoop<E> ClassYou will write a LinkedLoop<E> class (in a file named LinkedLoop.java) which implements the Loop<E> interface. In addition to the methods given in the Loop<E> interface, your LinkedLoop<E> class must have a constructor that takes no arguments and creates an empty loop. You may not add any other public constructors or methods. The internal data structure used by your LinkedLoop<E> must be a circular, doubly-linked chain of nodes. You may not use Java's LinkedList class for this assignment. You must implement your own chain of doubly-linked nodes. To implement the circular, doubly-linked chain of nodes, you will need to use the DblListnode<E> class (provided for you; see DblListnode.java). Your LinkedLoop<E> class will have a field of type DblListnode<E> that references the node representing the current item. You may include other private fields that you find helpful, but no public fields. Additional Related ClassesThere are two other classes that you will need to write to go along with your LinkedLoop<E> class: The EmptyLoopException classThe EmptyLoopException must be an unchecked exception. It is thrown by some methods (as described in the Loop<E> interface documentation). The LinkedLoopIterator<E> classThe Loop<E> interface includes an iterator() method that returns an Iterator<E> object. You must write a specialized iterator class, named LinkedLoopIterator<E>, which will be used as the type of iterator returned by the LinkedLoop<E>'s iterator() method. The LinkedLoopIterator<E> class must implement the Iterator<E> interface (you do not need to implement the remove method - just throw an UnsupportedOperationException). You will need to write a constructor for your LinkedLoopIterator<E>; a package-access constructor that takes a DblListnode<E> as a parameter is suggested. Remember that the purpose of an iterator is to provide a way to go through all the items in a collection exactly once. Make sure your LinkedLoopIterator is designed so that it starts with the current item and only goes through the items in the loop once. Message Loop Editor Menu of CommandsThe main method, in the file MessageLoopEditor.java, creates an empty Loop of messages and then prompts the user to enter commands, which it processes until the user types q for quit. The program prompts for input by displaying : enter command (? for help): If a valid command is entered, your program should carry out the command. The MessageLoopEditor.java file contains a partial implementation of the MessageLoopEditor class. Download this file and use it as the starting point for your MessageLoopEditor implementation. Note that the provided MessageLoopEditor class is set up to do all necessary validation of input: if an invalid command is given the program displays "invalid command" and then displays the prompt again. (You may assume that at least one non-whitespace character will always be inputted.) The program also ensures the following:
You do not need to change any of the provided processing of input. What you do need to do is provide the implementations of the unimplemented commands.
Note: Displaying the current context means displaying the message immediately before the current message, the current message, and the message immediately after the current message (one per line). For example, if the current message is "No traffic delays", the message before current is "Rain expected later tonight", and the message after current is "Current outside temp: 83 F", your program should display: Rain expected later tonight
===[ No traffic delays ]===
Current outside temp: 83 F
The "===[ ]===" are displayed to highlight the current message. However, if there are fewer than three messages in the loop, do the following:
TestingTesting interactive programs can be frustrating if you aren't careful about recording the commands that you've entered. A bug can suddenly occur and you may not recall the exact sequence of commands to reproduce the bug. A technique for testing interactive programs is to process a fixed set of commands from an input file. Input files can be developed that test particular aspects of the program; these tests are easily repeated by running the program again on a particular input file. The provided MessageLoopEditor has been written so that it can be provided with a single, optional, command-line argument that is the name of an input file containing message loop editor commands. If a command-line argument is not provided, then the program operates as an interactive console application reading commands from the console keyboard and displaying the results in the console window. If more than one command-line argument is given, the program displays "invalid command-line arguments" and quits. If a single command-line argument is provided, it is assumed to be the name of an input file. If the file doesn't exist or is unable to be opened, the program displays "problem with input file" and quits. The program assumes the file contains lines that start with at least one non-whitespace character and that the last line always has a single "q" for quit. How to proceedAfter you have read this program page and given thought to the problem we suggest the following steps:
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Handing inWhat should be handed in? Make sure your code follows the style and commenting standards used in CS 302 and CS 367. Electronically submit the following files to the Program 2 Dropbox on Learn@UW:
Please turn in only the file named above. Extra files clutter up the Dropbox directories. | ||||||||||||||||||||||||||||
| Last Updated: 8/21/2015 © 2015 Beck Hasti and Charles Fischer |