INST2002 Programming 2:
Support Sheet for Online Assessment 2
Set by: Luke Dickens
Available from 27th November, 2015
Due at 2pm on 8th December, 2015
Important Notice
This assessment forms part of your degree assessment. It must be done entirely
on your own from start to finish:
• You must not collaborate or work with other students at any stage.
• You must not send or show other students your answers.
• You must not ask other students for help, or ask to see their answers. As well as being
against regulations, this is unfair to the other student concerned, since it may lead to
them being accused of plagiarism.
• You must not seek help from friends, relatives, online discussion groups other than the
moodle forum for INST2002
• If you think any of the description of the task below is ambiguous or unclear, please
post to the moodle forum, explaining what your concerns are, or raise it in person with
your lecturer, Luke Dickens, or a INST2002 lab demonstrator.
• If you are unsure of any of the above points, please post your concern to the moodle
forum.
Finally, if there is any reason you do not think you can complete this assessment in
the alloted time, you should either make a formal request for an extension with your
home department, or discuss your reasons with the INST2002 lecturer, Luke Dickens at
l.dickens@ucl.ac.uk.
1 A Chat Room with a Profanity Filter
Imagine that you are asked to write code to support a collection of simple text based online
chat-rooms, with a configurable profanity filter. The chat-rooms consist of users posting
short text messages (posts), which are visible to others in the chat-room alongside the name
of the user who posted it. When reading these posts, some users will want profanities to be
filtered out, while some will not. For simplicity, we will assume that the list of profanities
1
are the same for all users and in all chat-rooms. However, it should be possible to add and
remove words from the profanity filter.
For example consider the following sequence of messages in a chat room whose name is
VictorianGents.
post order username text
0 “Raffles” “Hello Bunny, are you there?”
1 “Bunny” “Here I am, Raffles.”
2 “Raffles” “Excellent Bunny. Have you seen Dave
the nincompoop?”
3 “Dave” “How dare you call me a nincompoop, you
rapscallion.”
4 “Raffles” “Oh tish and pish Dave. Quit your
blithering, you twit.”
5 “Dave” “Zounds! You knave! I’ll not suffer
your insults further.”
6 “Raffles” “Gadzooks! Was it something I said
Bunny?”
Table 1: An example chat history for the VictorianGents chat-room.
Now, imagine that a technician has added the following terms to the profanity filter:
“blither”, “blithering”, “gadzooks”, “knave”, “pish”, “nincompoop”, “rapscallion”,
“tish”, “twit”, and “twits”.
Without the profanity filter switched on, the chat history for the VictorianGents chat
room would display to screen as shown in Figure 1:
Chat Room VictorianGents :
Raffles : Hello Bunny , are you there ?
Bunny : Here I am , Raffles .
Raffles : Excellent Bunny . Have you seen Dave the nincompoop ?
Dave : How dare you call me a nincompoop , you rapscallion .
Raffles : Oh tish and pish Dave . Quit your blithering , you twit .
Dave : Zounds ! You knave ! I ’ ll not suffer your insults further .
Raffles : Gadzooks ! Was it something I said Bunny ?
Figure 1: Unfiltered chat history for VictorianGents displayed to screen
If the same chat history were again displayed to screen, this time with the profanity filter
switched on, then it would appear as in Figure 2.
Note: All parts of the original text that match a word stored in the profanity filter has
had each character replaced with an asterisk, *, in the filtered text.
Note: The word “blithering” in Figure 1 has been replaced in Figure 2, with “**********”.
This is the case even though the shorter word “blither” is also in the list.
2
Chat Room VictorianGents [ filtered ]:
Raffles : Hello Bunny , are you there ?
Bunny : Here I am , Raffles .
Raffles : Excellent Bunny . Have you seen Dave the **********?
Dave : How dare you call me a ********** , you ***********.
Raffles : Oh **** and **** Dave . Quit your ********** , you ****.
Dave : ******! You *****! I ’ ll not suffer your insults further .
Raffles : ********! Was it something I said Bunny ?
Figure 2: Filtered chat history for VictorianGents displayed to screen
Note: If there is a choice between filtering one of two words, e.g. either “blither” or
“blithering”, then the longer profanity should be replaced with asterisks. If two equally
long profanity words overlap, then either word may be replaced with asterisks.
Note: The profanity filter should be case-insensitive, meaning that it should filter words
whether they appear in uppercase, lowercase or a mixture of cases, e.g. if “blithering” is
a profanity word, then it should filter “blithering”, “BLITHERING”, “Blithering”, and so
on.
Note: For simplicity, the profanity filter should filter any sequence of characters matching
a profanity, even if that word is contained within another word, e.g. if “tish” is a
profanity word then the text, “I am British”, should be filtered to be “I am Bri****”.
In a real world profanity filter, this may not be the preferred behaviour.
Finally, it should be possible to look at the history of just one user, with or without the
filter applied. For instance, if we wanted to see just Raffles history filtered and printed to
screen then it would appear as in Figure 3.
Chat Room VictorianGents [ filtered ]:
Raffles : Hello Bunny , are you there ?
Raffles : Excellent Bunny . Have you seen Dave the **********?
Raffles : Oh **** and **** Dave . Quit your ********** , you ****.
Raffles : ********! Was it something I said Bunny ?
Figure 3: Filtered chat history for VictorianGents displayed to screen
2 Your Task
In the code file Problem.java given to you, there are four classes: a public class Problem,
and three package visible classes Post, ProfanityFilter, and ChatRoom. The class Problem
has been written for you to test the code, and you do not need to edit this class. However,
you may choose to edit this class to test your changes as you go. The class Post has also
been written for you. Post is a very simple class that stores the user-name and text of a
chat-room post, and can convert these two pieces of information to a String. You must
3
not edit the class Post. You will need to edit the other two classes, ProfanityFilter
and ChatRoom. The required changes are described below.
2.1 The ProfanityFilter class
A ProfanityFilter object contains a collection of Strings each of which is a profanity, i.e.
a word that should be filtered out. It also provides methods for filtering out these profanities
in text. You should implement the following in ProfanityFilter.
• One or more fields to the ProfanityFilter class to store the Strings representing the
profanity words.
• A constructor, which takes no arguments and constructs an empty ProfanityFilter,
i.e. a ProfanityFilter with 0 profanity words contained in it.
• An addProfanity method, which takes a String as input, and includes it as a profanity
word.
• A removeProfanity method, which takes a String as input, and removes it from the
collection of a profanity words if it is present. Otherwise, it should do nothing.
• A getProfanities method, which takes no arguments and returns a String array of
all the profanities stored in the ProfanityFilter.
• A sortProfanitiesByLength method, which takes no arguments and sorts the profanities
by length, with the longest words appearing first and the shortest appearing
last. Two profanity words of the same length can appear in either order. After a
call to sortProfanitiesByLength, the getProfanities method should return the
profanities in length order.
• A static method filterWordInText, which takes two Strings as arguments: profanity
– a word which should be replaced with a dummy string of asterisks; and text – the
text in which profanity will be replaced. The method should return a string of filtered
text, i.e. text with every occurance of profanity replaced by a String of asterisks
of the same length.
For example, if text is the String “Quit your blithering, you twit.” and profanity
is the String “blithering”, then filterWordInText should return “Quit your
**********, you twit.”. You may find it helpful to use the method createDummyString
for filterWordInText.
Note: This method can be implemented with loops, or recursion. You will get extra
credit if you use recursion. However, you must not use the String methods indexOf,
or replace (or any other method containing the words indexOf or replace).
• A method filterText, which takes a String called text as argument and returns a
String which is a copy of the input text with all stored profanity words replaced by
asterisks.
Note: You should filter for the longest profanity words first.
4
2.2 The ChatRoom class
A ChatRoom object contains a collection of Posts in the order in which they were posted.
ChatRoom objects provide methods to get histories of filtered and unfiltered posts.
All ChatRoom objects have access to the same ProfanityFilter object, which they
can use to filter out bad-language. This ProfanityFilter can be accessed by the static
getProfanityFilter method, and set by the static setProfanityFilter method. Both
these methods are provided for you. Each ChatRoom also has two instance fields: the
roomName of type String, which is the name of the chat-room; and posts of type ArrayList<Post>,
which collects all messages posted to the chat-room. There are some other methods provided
for you too, see the code for details.
You will need to implement the following methods in ChatRoom:
• A constructor, which takes a single argument roomName of type String and stores this
as the chat-room name. This constructor should create a ChatRoom with 0 posts in its
history.
• A getRoomName method, which is a simple getter method for the roomName field.
• An addPost method, which takes two Strings as input: author – the author of the
post; and text – the text of the post. This method should store this information as a
Post.
• A getHistory method, which takes no arguments and returns a String array, containing
the unfiltered string representations of each post to the chat-room, in the order
they were added (by addPost).
• A getFilteredHistory method, which takes no arguments and returns a String
array, containing the filtered string representations of each post to the chat-room, in
the order they were added.
Note: Filtered posts are those that have been filtered by the ProfanityFilter. These
should filter both the author name and text of the post.
• A getAuthorHistory method, which takes a String argument author, and returns
a String array, containing the unfiltered string representations of each post to the
chat-room by author. Again, posts should be displayed in the order they were added.
• A getFilteredAuthorHistory method, which takes a String argument author, and
returns a String array, containing the filtered string representations of each post to
the chat-room by author. Again, posts should be displayed in the order they were
added.
Note: Filtered posts are those that have been filtered by the ProfanityFilter. These
should filter both the author name and text of the post.
3 Some Rules and Advice
You have been provided with signatures for all the methods described above in the code.
You should not change any of these signatures. In particular, for the methods provided in
the code:
5
• Do not change the return type.
• Do not change the visibility, e.g. public.
• Do not change the number or type of the input arguments.
• Do not change whether a method is static or not.
You may write your own additional methods, and you may add fields to the ProfanityFilter
and ChatRoom classes. In some cases, it may be easier to solve the problem if you define
helper methods, and you will be given credit if these are used appropriately.
You may find some of the standard Java library helpful to solve this problem. For
instance, the String class and its methods: length, toLowerCase, substring (2 overloaded
methods). getChar, and equals. You may also find the following methods in ArrayList
helpful: size, toArray, get, set, and remove. Make sure that you read up on how to use
these methods in the Java documentation. However, you must not use the String methods
indexOf, or replace (or any other method containing the words indexOf or replace), and
anyone using these methods will not get full marks for the associated task.
Finally, it is sometimes better to use an array and sometimes it is better to use an
ArrayList. You must decide when one is better than the other. You can always convert
from one to the other when needed.
4 A Local Copy of the Code
If you go to moodle, you can access a local copy of the code. This is the same code that will
appear in the text box when you finally log in to TestDome. You can experiment with this
local copy to test your ideas, before you log in to TestDome. Try compiling this local code
to start with, then running it to see what happens. At this point, try to make changes in
line with the description above, and recompile and run regularly to test your changes.
There is more than one way to solve this problem, and so long as you follow the instructions
and pass all the tests on TestDome you will be given a minimum of 80% overall1
.
Additional marks will be given for coding style and comments, up to a maximum of 20%.
This includes, but is not limited to: good names for variables, appropriate use of control
flow (e.g. for loops and if statements), meaningful and appropriate comments, minimising
duplication of code, appropriate helper methods, and consistent formatting of code.
1Note that if you use the forbidden methods indexOf, or replace (or any other method containing the
words indexOf or replace) then you will not get full marks for the associated task.
6

INST2002 Programming 2:
Support Sheet for Online Assessment 2
Set by: Luke Dickens
Available from 27th November, 2015
Due at 2pm on 8th December, 2015
Important Notice
This assessment forms part of your degree assessment. It must be done entirely
on your own from start to finish:
• You must not collaborate or work with other students at any stage.
• You must not send or show other students your answers.
• You must not ask other students for help, or ask to see their answers. As well as being
against regulations, this is unfair to the other student concerned, since it may lead to
them being accused of plagiarism.
• You must not seek help from friends, relatives, online discussion groups other than the
moodle forum for INST2002
• If you think any of the description of the task below is ambiguous or unclear, please
post to the moodle forum, explaining what your concerns are, or raise it in person with
your lecturer, Luke Dickens, or a INST2002 lab demonstrator.
• If you are unsure of any of the above points, please post your concern to the moodle
forum.
Finally, if there is any reason you do not think you can complete this assessment in
the alloted time, you should either make a formal request for an extension with your
home department, or discuss your reasons with the INST2002 lecturer, Luke Dickens at
l.dickens@ucl.ac.uk.
1 A Chat Room with a Profanity Filter
Imagine that you are asked to write code to support a collection of simple text based online
chat-rooms, with a configurable profanity filter. The chat-rooms consist of users posting
short text messages (posts), which are visible to others in the chat-room alongside the name
of the user who posted it. When reading these posts, some users will want profanities to be
filtered out, while some will not. For simplicity, we will assume that the list of profanities
1
are the same for all users and in all chat-rooms. However, it should be possible to add and
remove words from the profanity filter.
For example consider the following sequence of messages in a chat room whose name is
VictorianGents.
post order username text
0 “Raffles” “Hello Bunny, are you there?”
1 “Bunny” “Here I am, Raffles.”
2 “Raffles” “Excellent Bunny. Have you seen Dave
the nincompoop?”
3 “Dave” “How dare you call me a nincompoop, you
rapscallion.”
4 “Raffles” “Oh tish and pish Dave. Quit your
blithering, you twit.”
5 “Dave” “Zounds! You knave! I’ll not suffer
your insults further.”
6 “Raffles” “Gadzooks! Was it something I said
Bunny?”
Table 1: An example chat history for the VictorianGents chat-room.
Now, imagine that a technician has added the following terms to the profanity filter:
“blither”, “blithering”, “gadzooks”, “knave”, “pish”, “nincompoop”, “rapscallion”,
“tish”, “twit”, and “twits”.
Without the profanity filter switched on, the chat history for the VictorianGents chat
room would display to screen as shown in Figure 1:
Chat Room VictorianGents :
Raffles : Hello Bunny , are you there ?
Bunny : Here I am , Raffles .
Raffles : Excellent Bunny . Have you seen Dave the nincompoop ?
Dave : How dare you call me a nincompoop , you rapscallion .
Raffles : Oh tish and pish Dave . Quit your blithering , you twit .
Dave : Zounds ! You knave ! I ’ ll not suffer your insults further .
Raffles : Gadzooks ! Was it something I said Bunny ?
Figure 1: Unfiltered chat history for VictorianGents displayed to screen
If the same chat history were again displayed to screen, this time with the profanity filter
switched on, then it would appear as in Figure 2.
Note: All parts of the original text that match a word stored in the profanity filter has
had each character replaced with an asterisk, *, in the filtered text.
Note: The word “blithering” in Figure 1 has been replaced in Figure 2, with “**********”.
This is the case even though the shorter word “blither” is also in the list.
2
Chat Room VictorianGents [ filtered ]:
Raffles : Hello Bunny , are you there ?
Bunny : Here I am , Raffles .
Raffles : Excellent Bunny . Have you seen Dave the **********?
Dave : How dare you call me a ********** , you ***********.
Raffles : Oh **** and **** Dave . Quit your ********** , you ****.
Dave : ******! You *****! I ’ ll not suffer your insults further .
Raffles : ********! Was it something I said Bunny ?
Figure 2: Filtered chat history for VictorianGents displayed to screen
Note: If there is a choice between filtering one of two words, e.g. either “blither” or
“blithering”, then the longer profanity should be replaced with asterisks. If two equally
long profanity words overlap, then either word may be replaced with asterisks.
Note: The profanity filter should be case-insensitive, meaning that it should filter words
whether they appear in uppercase, lowercase or a mixture of cases, e.g. if “blithering” is
a profanity word, then it should filter “blithering”, “BLITHERING”, “Blithering”, and so
on.
Note: For simplicity, the profanity filter should filter any sequence of characters matching
a profanity, even if that word is contained within another word, e.g. if “tish” is a
profanity word then the text, “I am British”, should be filtered to be “I am Bri****”.
In a real world profanity filter, this may not be the preferred behaviour.
Finally, it should be possible to look at the history of just one user, with or without the
filter applied. For instance, if we wanted to see just Raffles history filtered and printed to
screen then it would appear as in Figure 3.
Chat Room VictorianGents [ filtered ]:
Raffles : Hello Bunny , are you there ?
Raffles : Excellent Bunny . Have you seen Dave the **********?
Raffles : Oh **** and **** Dave . Quit your ********** , you ****.
Raffles : ********! Was it something I said Bunny ?
Figure 3: Filtered chat history for VictorianGents displayed to screen
2 Your Task
In the code file Problem.java given to you, there are four classes: a public class Problem,
and three package visible classes Post, ProfanityFilter, and ChatRoom. The class Problem
has been written for you to test the code, and you do not need to edit this class. However,
you may choose to edit this class to test your changes as you go. The class Post has also
been written for you. Post is a very simple class that stores the user-name and text of a
chat-room post, and can convert these two pieces of information to a String. You must
3
not edit the class Post. You will need to edit the other two classes, ProfanityFilter
and ChatRoom. The required changes are described below.
2.1 The ProfanityFilter class
A ProfanityFilter object contains a collection of Strings each of which is a profanity, i.e.
a word that should be filtered out. It also provides methods for filtering out these profanities
in text. You should implement the following in ProfanityFilter.
• One or more fields to the ProfanityFilter class to store the Strings representing the
profanity words.
• A constructor, which takes no arguments and constructs an empty ProfanityFilter,
i.e. a ProfanityFilter with 0 profanity words contained in it.
• An addProfanity method, which takes a String as input, and includes it as a profanity
word.
• A removeProfanity method, which takes a String as input, and removes it from the
collection of a profanity words if it is present. Otherwise, it should do nothing.
• A getProfanities method, which takes no arguments and returns a String array of
all the profanities stored in the ProfanityFilter.
• A sortProfanitiesByLength method, which takes no arguments and sorts the profanities
by length, with the longest words appearing first and the shortest appearing
last. Two profanity words of the same length can appear in either order. After a
call to sortProfanitiesByLength, the getProfanities method should return the
profanities in length order.
• A static method filterWordInText, which takes two Strings as arguments: profanity
– a word which should be replaced with a dummy string of asterisks; and text – the
text in which profanity will be replaced. The method should return a string of filtered
text, i.e. text with every occurance of profanity replaced by a String of asterisks
of the same length.
For example, if text is the String “Quit your blithering, you twit.” and profanity
is the String “blithering”, then filterWordInText should return “Quit your
**********, you twit.”. You may find it helpful to use the method createDummyString
for filterWordInText.
Note: This method can be implemented with loops, or recursion. You will get extra
credit if you use recursion. However, you must not use the String methods indexOf,
or replace (or any other method containing the words indexOf or replace).
• A method filterText, which takes a String called text as argument and returns a
String which is a copy of the input text with all stored profanity words replaced by
asterisks.
Note: You should filter for the longest profanity words first.
4
2.2 The ChatRoom class
A ChatRoom object contains a collection of Posts in the order in which they were posted.
ChatRoom objects provide methods to get histories of filtered and unfiltered posts.
All ChatRoom objects have access to the same ProfanityFilter object, which they
can use to filter out bad-language. This ProfanityFilter can be accessed by the static
getProfanityFilter method, and set by the static setProfanityFilter method. Both
these methods are provided for you. Each ChatRoom also has two instance fields: the
roomName of type String, which is the name of the chat-room; and posts of type ArrayList<Post>,
which collects all messages posted to the chat-room. There are some other methods provided
for you too, see the code for details.
You will need to implement the following methods in ChatRoom:
• A constructor, which takes a single argument roomName of type String and stores this
as the chat-room name. This constructor should create a ChatRoom with 0 posts in its
history.
• A getRoomName method, which is a simple getter method for the roomName field.
• An addPost method, which takes two Strings as input: author – the author of the
post; and text – the text of the post. This method should store this information as a
Post.
• A getHistory method, which takes no arguments and returns a String array, containing
the unfiltered string representations of each post to the chat-room, in the order
they were added (by addPost).
• A getFilteredHistory method, which takes no arguments and returns a String
array, containing the filtered string representations of each post to the chat-room, in
the order they were added.
Note: Filtered posts are those that have been filtered by the ProfanityFilter. These
should filter both the author name and text of the post.
• A getAuthorHistory method, which takes a String argument author, and returns
a String array, containing the unfiltered string representations of each post to the
chat-room by author. Again, posts should be displayed in the order they were added.
• A getFilteredAuthorHistory method, which takes a String argument author, and
returns a String array, containing the filtered string representations of each post to
the chat-room by author. Again, posts should be displayed in the order they were
added.
Note: Filtered posts are those that have been filtered by the ProfanityFilter. These
should filter both the author name and text of the post.
3 Some Rules and Advice
You have been provided with signatures for all the methods described above in the code.
You should not change any of these signatures. In particular, for the methods provided in
the code:
5
• Do not change the return type.
• Do not change the visibility, e.g. public.
• Do not change the number or type of the input arguments.
• Do not change whether a method is static or not.
You may write your own additional methods, and you may add fields to the ProfanityFilter
and ChatRoom classes. In some cases, it may be easier to solve the problem if you define
helper methods, and you will be given credit if these are used appropriately.
You may find some of the standard Java library helpful to solve this problem. For
instance, the String class and its methods: length, toLowerCase, substring (2 overloaded
methods). getChar, and equals. You may also find the following methods in ArrayList
helpful: size, toArray, get, set, and remove. Make sure that you read up on how to use
these methods in the Java documentation. However, you must not use the String methods
indexOf, or replace (or any other method containing the words indexOf or replace), and
anyone using these methods will not get full marks for the associated task.
Finally, it is sometimes better to use an array and sometimes it is better to use an
ArrayList. You must decide when one is better than the other. You can always convert
from one to the other when needed.
4 A Local Copy of the Code
If you go to moodle, you can access a local copy of the code. This is the same code that will
appear in the text box when you finally log in to TestDome. You can experiment with this
local copy to test your ideas, before you log in to TestDome. Try compiling this local code
to start with, then running it to see what happens. At this point, try to make changes in
line with the description above, and recompile and run regularly to test your changes.
There is more than one way to solve this problem, and so long as you follow the instructions
and pass all the tests on TestDome you will be given a minimum of 80% overall1
.
Additional marks will be given for coding style and comments, up to a maximum of 20%.
This includes, but is not limited to: good names for variables, appropriate use of control
flow (e.g. for loops and if statements), meaningful and appropriate comments, minimising
duplication of code, appropriate helper methods, and consistent formatting of code.
1Note that if you use the forbidden methods indexOf, or replace (or any other method containing the
words indexOf or replace) then you will not get full marks for the associated task.
6