本次Java代写是完成一个商品销售的控制台程序
COSC1295 Advanced Programming, S1, 2020

Assessment Criteria
This assessment will determine your ability to implement Object-Oriented Java code according to the
specifications shown below. In addition to functional correctness (i.e. getting your code to work) you will also
be assessed on code quality. Specifically:
● You should aim to provide high cohesion and low coupling.
● You should aim for maximum encapsulation and information hiding.
● You should rigorously avoid code duplication.
● You should use superclass methods to retrieve and/or manipulate superclass properties from within
subclass methods where necessary.
● You should take advantage of polymorphism wherever possible when invoking methods upon objects
that have been created.
● You should comment important sections of your code remembering that clear and readily
comprehensible code is preferable to a comment.
3. Learning Outcomes
This assessment is relevant to the following Learning Outcomes:
CL01: use the Java programming language in the implementation of small to medium sized application
programs that illustrate professionally acceptable coding and performance standards.
CL02: demonstrate knowledge of the basic principles of the object-oriented development process and apply
this understanding to the analysis and design of solutions for small to medium scale problems.
CLO3: describe and apply basic algorithms and data structures, in particular simple searching and sorting of
data stored in data structures and manipulating data.
4. Assessment details
The UniLink system allows students to create and publish many types of posts. All those posts share a set of
common attributes and methods and also have their own different sets of attributes and behaviors. The
following sections describe the requirements of the Post superclass and its subclasses that you must
implement in your code.
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Post class
● Id: a string which uniquely identifies each post. The UniLink system must generate a unique id for each
newly created post according to the following format:
○ An event post id begins with the string “EVE” followed by a three-digit, zero-padding number.
The first event post has id EVE001, the subsequent event posts have id EVE002, EVE003,
EVE004, EVE005…
○ A sale post id begins with the string “SAL” followed by a three-digit, zero-padding number.
The first sale post has id SAL001, the subsequent sale posts have ids SAL002, SAL003,
SAL004, SAL005…
○ A job post id begins with the string “JOB” followed by a three-digit, zero-padding number. For
example, the first job post has id JOB001, the subsequent job posts have id JOB002,
JOB003, JOB004, JOB005…
● Title: a short string to summarise the post. It can be a name of an event in an event post, or name of
an item in a sale post or name of a job in a job post.
● Description: a longer string which provides more information about the post. It can be a description of
an event, or an item on sale or a job specification.
● Creator id: a string which is the id of the student who created the post in the UniLink system. Student
id begins with the character ‘s’ followed by a number, for example, s1, s2, s3… are all acceptable
student id in this assignment.
● Status: indicates whether the post is open to receive replies or closed and no longer accepts replies. In
your implementation, you must make sure that a post status can only be either OPEN or CLOSED.
● Replies: a data structure of your choice, for example an array or array list, to store all replies to a post.
Each reply is an object of the Reply class. More details about this class are shown in the “Reply class”
section further down this document.
Constructors
At least one constructor to initialize all attributes shown above. By default, a post status is set to OPEN
when a post is created.
Your implementation should not allow constructors in the Post class to be used directly to create Post
objects. Instead, these constructors should only be called in constructors of subclasses of the Post
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class, such as the Event, Sale and Job classes (more details below). Remember that one of our
objectives is to reduce code duplication, especially when initializing common attributes of all post
objects.
Methods
public String getPostDetails()
This method should build and return a string which contains information about a post. In this
Post class, which is a superclass, the getPostDetails method only build and return a string
containing the post id, title, description, creator id and status, which are common attributes of
all types of post as shown above. This method is overridden in subclasses of the Post class to
add more specific details relevant to each type of post, which will be described in the next
sections.
The returned string should be formatted in a human readable form as shown in the examples
below.
Example: calling the method getPostDetails() on an event post object will return the following
String:
ID: EVE001
Title: Movie on Sunday
Description: Join us to see a movie this
Sunday with ticket
discounts applied to all
group members!
Creator ID: s3456223
Status: OPEN
Note: details about event
id, title, description, creator
id and status are obtained
by calling the
getPostDetails() of the Post
class.
Venue: Village Cinema
Date: 29/03/2020
Capacity: 3
Attendees: 0
The getPostDetails()
method must be
overridden in the Event
subclass of the Post class to
display more specific
details about the event
such as venue, date,
capacity and the current
number of attendees.
More in the Event class
specifications below.
Abstract methods
public abstract boolean handleReply(Reply reply)
Each type of post has a different way to handle a reply, therefore in this Post class, which is the
superclass, this method is set to abstract and will be implemented in concrete subclasses of the
Post class, i.e. in Event, Sale and Job classes
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This method receives a reference to a Reply object, which store all details of a reply to this
post. Specifications of the Reply class are shown in the “Reply class” section further down. This
method returns true to indicate that the reply is processed and added to the collection of
replies. The method returns false otherwise. More details about the implementation of this
method are described in subclasses of the Post class in the sections further down this
document.
public abstract String getReplyDetails()
This method should only be called by the post creator on their own posts. It returns a String
containing details of all replies to that post. Each type of post has a different way to display
reply details to the post creator, therefore this method must be set to abstract in this Post class
and overridden in subclasses of the Post class. More details about how this method should be
implemented will be shown in later sections.
Accessor and mutator methods
Simple accessor and mutator methods must be implemented in this Post class. You should only
implement necessary accessor and mutator methods according to the Post class attributes shown
above. There must be no redundant accessor and mutator methods in your code.
Reply class
When a student replies to a post, the following information is stored in an object of the Reply class:
● Post id: the id of the post which the reply is associated with.
● Value: a decimal number. For the sake of simplicity, in this assignment, a responder needs to enter a
positive value as part of a reply to a post. Specifically, your program should require a responder to
enter value 1 to join an event in an event post, or a price he or she is willing to pay for an item in a sale
post or an amount of money he or she wants to be paid to complete the job advertised in a job post.
See also the sale rules and job rules in the sections below.
● Responder id: the id of the student who replies.
You’re required to implement at least one constructor to initialize all the attributes shown above when a reply
object is created.
You also need to implement simple accessor and mutator methods according to the attributes shown above.
Event class
A student participated in the UniLink system can create an event post to let other students know about an
upcoming event. An event post is an object of the Event class, which is a concrete subclass of the abstract Post
class. In addition to common information of a post such as id, title, description, creator id, status, replies as
shown in the Post superclass, an event post object also stores the following information:
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● Venue: a value of type String which is the location of the event
● Date: the date when the event happens. For simplicity, no need to store the event time. It is sufficient
to use a value of type String to store a date in the format dd/mm/yyyy, for example 20/03/2020.
● Capacity: an integer which is the maximum number of attendees of the event
● Attendee count: the current number of participants in the event. A newly created event has zero
attendee count. When a student selects to join the event, attendee count increments by one. When
the attendee count is equal to event capacity, the UniLink system will automatically close the event,
i.e. the event status set to CLOSED. A closed event no longer accepts participants.
Constructors
At least one constructor to initialize all attributes shown above. When a new event post is created, the
creator will enter an event name, description, venue, date, capacity. The UniLink system will generate
a new unique event post id and set that id and creator id to the newly created post object.
To reduce code duplication, your implementation must make use of the constructors created in the
Post superclass.
Methods
public String getPostDetails()
You must override this method, which is inherited from the superclass Post, to return a String
containing all common details of a post as shown in the Post class, and additional details of an
event post, i.e. venue, date, capacity and attendees according to the following example:
Example: output of a getPostDetails() method call on an event post object
ID: EVE001
Title: Programming Study Group Wednesday night
Description: Let’s meet this Wednesday afternoon to finish
the programming assignment!
Creator ID: s3477223
Status: OPEN
Venue: RMIT Library
Date: 15/04/2025
Capacity: 5
Attendees: 0
public boolean handleReply(Reply reply)
Your Event class must implement this abstract handleReply method shown previously in the
Post class to handle a reply to an event post. When a student replies to an event post to join an
event, details of that reply are stored in a Reply object passed to this method (see “Reply class”
section). If the reply is valid, the event is not full and the student id is not yet recorded in that
event, then this handleReply method must add this reply object to the replies collection of this
event post and return true, otherwise the reply will not be added to the replies collection and a
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false value is returned. When the event is full, i.e when the number of attendees is equal to
capacity, event status is set to CLOSED.
public String getReplyDetails()
As shown in the Post class, this method should only be called by the post creator on their own
posts. It returns a String containing details of all replies to that post. When calling this method
on an event post, this method must return a comma-separated string of the ids of students
who have sent replies to join the event and have been accepted by the system as attendees,
according to the following format:
Attendee list: [comma-separated string of attendee id values]
If an event has no attendee, then your method should return the following string:
Attendee list: Empty
Example: when an event post creator chooses to view his own events, in addition to details of
the posts as shown in the getPostDetails method requirements, the getReplyDetails method
will also be called to return a string as shown below (in each event post, notice the status,
capacity, attendees and attendee list fields below):
ID: EVE001
Title: Programming Study Group Wednesday night
Description: Let’s meet this Wednesday afternoon to
finish the programming assignment
Owner ID: s3477223
Status: OPEN
Venue: RMIT Library
Date: 15/04/2020
Capacity: 5
Attendees: 0
Attendee list: Empty
—————————-
Title: Movie on Sunday
Description: See a movie this Sunday with a ticket
discount applied to all group members.
Owner ID: s3477223
Status: CLOSED
Venue: Village Cinema
Date: 26/03/2020
Capacity: 4
Attendees: 4
Attendee list: s3488456,s3599643,s3737458,s3483921
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Accessor and mutator methods
Simple accessor and mutator methods must be implemented in this Event class. You should only implement
necessary accessor and mutator methods according to the additional attributes shown above. There must be
no redundant accessor and mutator methods in your code.
Sale class
When a student has an item to sell, he or she can create a sale post in the UniLink system to let other students
know about the features of the item. Other students who are interested in that item can reply with an offer
price they want to pay for the item.
In addition to common information of a post such as id, title, description, creator id, status and a replies
collection as described in the Post superclass, a sale post object also stores the following information:
● Asking price: the price at which the post creator wants to sell the item. This asking price is not visible
to other students (see the Sale post rules section below for more details).
● Highest offer: the highest price offered among all replies from students interested to buy the item.
● Minimum raise: the minimum amount by which a new offer price in a reply must be higher than the
highest offer recorded in this sale post (see Sale post rules section below for more details).
Sale post rules
There is a special feature about this type of sale. Specifically, the asking price is not visible to students viewing
the sale post. When a student views a sale post which is opened, he or she can only see the item name,
description and the highest price offered at that point, and then chooses whether to reply with an offer price.
The UniLink system only accepts a reply to a sale post when the post is opened (i.e. post status is OPEN) and
will process the new offer price in a reply according to the following rules:
• If the new offer price is less than or equal to the current highest offer, then the system rejects that
offer price.
• If the new offer price is greater than the highest offer, then the system accepts the new offer price and
set the highest offer value to the new offer price. At this point, if this new offer price is greater than or
equal to the asking price, then the system will close the sale post and display a message telling the
responder that the item has been sold to him or her.
Constructors
At least one constructor to initialize all attributes shown above. When a new sale post is created, the
creator will enter the item name, description, asking price and minimum raise. The UniLink system will
generate a new unique sale post id and set that id and creator id to the newly created sale post object.
To reduce code duplication, your implementation must make use of the constructors created in the
Post superclass.
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Methods
public String getPostDetails()
You must override this method, which is inherited from the superclass Post, to return a String
containing all common details of a post as shown in the Post class, and additional details of a
sale post which are the minimum raise and highest offer according to the following example:
Example: output of a getPostDetails() method call on a sale post object, which hasn’t yet
received any offer
ID: SAL001
Title: IPad Air 2 64GB
Description: Excellent working condition, comes with box,
cable and charger.
Creator ID: s3456223
Status: OPEN
Minimum raise: $15.00
Highest offer: NO OFFER
public boolean handleReply(Reply reply)
Your Sale class must implement this abstract handleReply method inherited from the Post
superclass to handle a reply to a sale post. When a reply with a valid offer price is given, this
method must add that reply to the replies collection and close the post if the price offer is
greater than or equal to the asking price of the item. This method returns false to indicate that
the given reply has a price offer which is not valid and that reply will not be kept in the replies
collection.
public String getReplyDetails()
As shown in the Post class, this method should only be called by the post creator on their own
posts. It returns a String containing details of all replies to that post. When calling this method
on a sale post, this method must return the list of replies sorted in descending order of offer
prices as shown in the example below:
Example: when a sale post creator chooses to view his own sale post, in addition to details of
the post as shown in the getPostDetails method requirements, the post creator also sees the
asking price. Furthermore, the getReplyDetails method is also called to display the Offer History
section shown below. There are 5 replies sorted in descending order of offer prices. The highest
offer is above the asking price, therefore the post is closed and the item is sold to the
corresponding responder, the student s4.
ID: SAL001
Title: IPad Air 2 64GB
Description: Excellent working condition, comes with box,
cable and charger.
Creator ID: s3456223
Status: CLOSED
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Minimum raise: $15.00
Highest offer: 305.00
Asking price: $300.00 (NOTE: only visible to the post creator)
— Offer History —
s4: $305.00
s5: $290.00
s3: $250.00
s2: $180.00
s1: $100.00
Accessor and mutator methods
Simple accessor and mutator methods must be implemented in this Sale class. You should only implement
necessary accessor and mutator methods according to the additional attributes shown above. There must be
no redundant accessor and mutator methods in your code.
Job class
This is another type of post to enable the post creator to describe a job which he or she needs to hire
someone to do and the price at which the post creator expects to pay. Other students can see this job post in
the system and reply with different prices they want to get paid to complete the job.
In addition to common information of a post such as id, title, description, creator id, status and a replies
collection as shown in the Post superclass, a job post object also stores the following information:
● Proposed price: the maximum amount of money the job post creator is willing to paid for the job.
● Lowest offer: the lowest amount offered among all replies from students interested in taking this job.
Job post rules
The UniLink system only accepts a reply to a job post when the post is opened (i.e. post status is OPEN) and
will process the new offer price in a reply according to the following rules:
• If the new offer price is greater than or equal to the current lowest offer, then the system rejects that
new offer price.
• If the new offer price is less than the current lowest offer, then the system accepts the new offer price
and set the current lowest offer value to the new offer price.
• The system will not automatically close a job post. The creator of the job post will manually close the
job post and select a responder with the lowest offer price.
Constructors
At least one constructor to initialize all attributes shown above. When a new job post is created, the
creator will enter the job name, description and proposed price. The UniLink system will generate a
new unique job post id and set that id and creator id to the newly created job post object.
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To reduce code duplication, your implementation must make use of the constructors created in the
Post superclass.
Methods
public String getPostDetails()
You must override this method, which is inherited from the superclass Post, to return a String
containing all common details of a post as shown in the Post class, and additional details of a
job post, which are the proposed price and lowest offer according to the following example:
Example: output of a getPostDetails() method call on a job post object, which has already got a
number of offer prices, only the lowest offer is shown:
ID: JOB001
Title: Moving House
Description: Need a person to help me move my belongings to a
new house
Creator ID: s3
Status: OPEN
Proposed price: $190.00
Lowest offer: $180.00
public boolean handleReply(Reply reply)
Your Job class must implement this abstract handleReply method inherited from the Post
superclass to handle a reply to a job post. When a reply with a valid offer price is given
according to the Job post rules above, this method must add that reply to the replies collection.
This method returns false in cases when a given reply cannot be accepted according to the Job
post rules above
public String getReplyDetails()
As shown in the Post class, this method should only be called by the post creator on their own
posts. It returns a String containing details of all replies to that post. When calling this method
on a job post, this method must return the list of replies sorted in ascending order of offer
prices as shown in the example below:
Example: when a job post creator chooses to view his own job post, in addition to details of the
post as shown in the getPostDetails method requirements, the getReplyDetails method is also
called to display the Offer History section shown below. There are 4 replies sorted in ascending
order of offer prices.
ID: JOB001
Title: Moving House
Description: Need a person to help me move my belongings to a
new house
Creator ID: s3545897
Status: OPEN
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Proposed price: $190.00
Lowest offer: 165.00
— Offer History —
s4: $165.00
s3: $178.00
s2: $180.00
s1: $185.00
Accessor and mutator methods
Simple accessor and mutator methods must be implemented in this Job class. You should only implement
necessary accessor and mutator methods according to the additional attributes shown above. There must be
no redundant accessor and mutator methods in your code.
Implementing the UniLink system class
In Assignment 1, the UniLink system class is a console application. All user interactions with the system will be
via a menu described below. In Assignment 2, you will create a graphical user interface of this system using
JavaFx.
You are required to implement a class named UniLink which contains a single collection of type Post to store
post objects of the three types, i.e. Event, Sale and Job posts. Posts and replies will be created by users at
runtime by selecting options shown in the menus shown below.
Your implementation must propose code reuse, reduce code duplication and apply polymorphism correctly,
especially when calling methods such as handleRely, getPostDetails and getReplyDetails on post objects.
When your program is executed, a user will be asked to login. After logging in, the main menu will appear as
shown in the example below. To make it easier for testing, we don’t use password, just need a student
number to log in.
Assumption: in this assignment, assume that only one user can log in at a time.
Example: a student with the username ‘s1’ logs in to the UniLink system and is presented with the UniLink
System menu with the following two options:
** UniLink System **
1. Log in
2. Quit
Enter your choice: 1
Enter username: s1
As shown above, the user has logged in as student s1. Then the Student Menu is displayed:
Welcome s1!
** Student Menu **
1. New Event Post
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2. New Sale Post
3. New Job Post
4. Reply To Post
5. Display My Posts
6. Display All Posts
7. Close Post
8. Delete Post
9. Log Out
Enter your choice:
To execute a feature of the system as shown in the menu above, the user needs to enter the number at the
beginning of the corresponding menu item. If an invalid number is entered, an error message should be
displayed, and the menu should be re-displayed. When a valid number is entered, your program should
execute the corresponding method and then return to this student menu. Your program must stop when the
user chooses to log out and quit the application.
This is a console application so all output data should be printed to the standard output.
Following is a description of each feature provided by the menu above:
Adding a new Event/Sale/Job post
From the student menu shown above, a student selects option 1, 2, 3 to add a new Event, Sale, Job post
respectively. When a new post is created, your program must meet the following requirements:
● You program needs to ask the user for the correct information depending on the type of post.
● When the new post is created and saved successfully in the system, your program must show a
message to let the user know about the id of the newly created post.
● User input validation must be implemented to make sure the user enters correct details for all the
post.
Example: creating an event post
[Student menu]
Enter your choice: 1
Enter details of the event below:
Name: Friday night out
Description: Let’s meet this Friday
Venue: Melbourne Central
Date: 10/04/2020
Capacity: 5
Success! Your event has been created with id EVE001
[Student menu is shown again]
Example: creating a sale post
[Student menu]
Enter your choice: 2
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Enter details of the item to sale below:
Name: 13-inch Macbook Pro 2018 sale
Description: In good condition, ready to use
Asking price: 1850
Minimum raise: 40
Success! Your new sale has been created with id SAL001
[Student menu is shown again]
Example: creating a job post
Enter your choice: 3
Enter details of the job below:
Name: Moving House
Description: Need a person to help me move my belongings to a
new house
Propose price: 90
Success! Your job has been created with id JOB001
[Student menu is shown again]