OOP Lab Task 2

Required Tutorials

• The Object Oriented Paradigm; Classes and Objects
• Notions About the Java Language
• Writing and Executing a Java Program
• Java Syntax; A Program's Lexical Structure
• Coding Conventions

Requirements

• Create a Java application project, or open your previous one.
• Add to your project the class Message exactly as defined in OOP Lab Task 1.
• Add another class, named Inbox, that encapsulates an array of Message objects and treats them as a queue of messages. The Inbox class fields are:
  • a reference (immutable) to an array of Message objects;
  • two integers that denotes the head of the queue (that points to the oldest unread message) and its tail (the place where the next message will be stored);
• All fields are private. The queue is handled only through the public methods of this class.
• Add to the Inbox class a constructor that instantiates the encapsulated array of Messages, whose length is given as the constructor's sole argument. This constructor sets also the head and the tail of the message queue.
• Add a method, named add, which does not return anything and has only one argument, a Message. This method adds the new message to the queue by setting the element at the tail to point to it. Then advances the tail to the next element of the array. If the queue is already full the message is not added and the method outputs "The inbox is full" on the screen.
• Add a method, named read, which takes no argument and returns a reference to the oldest unread message. It also advances the head of the queue to the next unread message. If the inbox is empty, the method returns no reference and outputs "The inbox is empty" on the screen.
• The head and tail indexes wrap around to the first element of the array after they reach it's last element (the queue is implemented as a circular buffer).
• The third method, named list, does not change the queue at all and returns a string that is formatted in the following way. If the queue is empty the method returns the string "There are no messages in inbox". Otherwise the first line is "Inbox messages from:" followed by one line for each message in the inbox, starting from the oldest message down to the newest. The lines are numbered and on each line appears only the name of the sender of that message. For example, if three messages are received from George, Mary and Andrew, the returned string, when printed on the screen must be:

Inbox messages from:
1 George
2 Mary
3 Andrew

• The listed numbers show the order of the messages from the oldest one to the newest. They do not necessarily correspond to the actual indexes in the array!
• Write another class called Main (the default class created if you created a project within NetBeans), which should contain only the main method, which instantiates a small inbox, let's say of 3 or 4 locations, and play than at will with adding to, reading from, and listing the inbox. You may create separately some messages or you may instantiate them right in the call of the ad method:

inbox.add(new Message("Mary","Hello everybody!"));, where the constructor returns exactly the type of argument that the ad method expects.

• Test also the inbox for the limit cases, trying inside the main method to read from an empty inbox, to write into a full inbox, or to list an empty one.

Submitting

• The assignment will be evaluated automatically by the Web-CAT platform.
• You could access the Web-CAT platform using the username and the password with which you acces the electronica.curs.pub.ro intranet.
• Select the OOP Lab Task 2 assignment.
• Submit your work as a single .zip archive (give it whatever name you choose) containing only the Java source code files.
• Attention Any deviation from these instructions may lead to the loss of the entire amount of points.