Description
In this assignment, you will simulate an on-line music centre called the MusicExchangeCenter where Users log in and download Songs from other users’ computers. It is a similar idea to the operation of the original Napster program that operated many years ago where users shared songs. You won’t be doing any downloading or internet programming. Instead, you will just simulate what happens in real life. The assignment will give you familiarity with ArrayLists and HashMaps. To get started with the assignment, download the Assignment4-Starting-Code.zip file from the assignment page, which contains an IntelliJ project with a number of classes that will be used in the assignment. (1) The Song/ User Classes The Song and User classes represent a song that is available at the Music Exchange Center and a user of the Music Exchange Center that logs in to download music. Do the following in the User class: Add a songList attribute which is an ArrayList of Song objects. This list will contain all the songs that this user has on his/her hard drive to be made available to the Music Exchange Center community. Adjust the 2nd constructor to ensure that this attribute is initialized properly. Write a get method for the attribute as well. Adjust the toString() method so that the XXX is replaced by the number of songs available in the user’s song list. Create a method called addSong(Song s) which adds a given song to the user’s song list. Create a method called totalSongTime() that returns an integer indicating the total duration (i.e., amount of time), in seconds, that all of the user’s songs would require if played. COMP 1406 – W20 – A4 Due Friday, March 20th at 11:59 PM Due Friday, March 20th at 11:59 PM (2) The MusicExchangeCenter Class Implement a class called MusicExchangeCenter which represents the company website that users log in and out of in order to download music. The class should have this attribute: users – an ArrayList of all registered Users (which may be either logged on or not logged on). Create the following methods: A zero-parameter constructor that sets attributes properly. An onlineUsers() method that returns an ArrayList of all Users that are currently online. Note that this method creates and returns a new ArrayList each time it is called. An allAvailableSongs() method that returns a new ArrayList of all Songs currently available for download (i.e., all songs that are available from all logged-on users). Note that this method creates and returns a new ArrayList each time it is called. A toString() method that returns a string representation of the music center showing the number of users currently online as well as the number of songs currently available. (e.g., “Music Exchange Center (3 users on line, 15 songs available)”). A userWithName(String s) method that finds and returns the user object with the given name if it is in the list of users. If not there, null should be returned. A registerUser(User x) method that adds a given User to the music center’s list of users, provided that there are no other users with the same userName. If there are other users with the same userName, then this method does nothing. Use the userWithName(String s) method above. An availableSongsByArtist(String artist) method that returns a new ArrayList of all Songs currently available for download by the specified artist. Note that this method creates and returns a new ArrayList each time it is called. Go back to the User class and add these methods: A register(MusicExchangeCenter m) that makes use of the registerUser(User x) method that you just wrote to register the user into the given MusicExchangeCenter m. (Note that this should be a one-line method). A logon() method that simulates a user going online. A logoff() method that simulates a user going offline. Now you should test your code. To do so, run the MusicExchangeTestProgram.java file and compare your results to the expected results below. COMP 1406 – W20 – A4 Due Friday, March 20th at 11:59 PM Due Friday, March 20th at 11:59 PM Here is the output that you should see: Status: Music Exchange Center (0 users on-line, 0 songs available) On-Line Users: [] Available Songs: [] Status: Music Exchange Center (2 users on-line, 8 songs available) On-Line Users: [Disco Stew: 4 songs (online), Ronnie Rocker: 4 songs (online)] Available Songs: [“Hey Jude” by The Beatles 4:35, “Barbie Girl” by Aqua 3:54, “Only You Can Rock Me” by UFO 4:59, “Paper Soup Cats” by Jaw 4:18, “Rock is Cool” by Yeah 4:17, “My Girl is Mean to Me” by Can’t Stand Up 3:29, “Only You Can Rock Me” by UFO 4:52, “We’re Not Gonna Take It” by Twisted Sister 3:9] Status: Music Exchange Center (4 users on-line, 16 songs available) On-Line Users: [Disco Stew: 4 songs (online), Ronnie Rocker: 4 songs (online), Country Candy: 3 songs (online), Peter Punk: 5 songs (online)] Available Songs: [“Hey Jude” by The Beatles 4:35, “Barbie Girl” by Aqua 3:54, “Only You Can Rock Me” by UFO 4:59, “Paper Soup Cats” by Jaw 4:18, “Rock is Cool” by Yeah 4:17, “My Girl is Mean to Me” by Can’t Stand Up 3:29, “Only You Can Rock Me” by UFO 4:52, “We’re Not Gonna Take It” by Twisted Sister 3:9, “If I Had a Hammer” by Long Road 4:15, “My Man is a 4×4 Driver” by Ms. Lonely 3:7, “This Song is for Johnny” by Lone Wolf 4:22, “Bite My Arms Off” by Jaw 4:12, “Where’s My Sweater” by The Knitters 3:41, “Is that My Toenail ?” by Clip 4:47, “Anvil Headache” by Clip 4:34, “My Hair is on Fire” by Jaw 3:55] Available Songs By Jaw: [“Paper Soup Cats” by Jaw 4:18, “Bite My Arms Off” by Jaw 4:12, “My Hair is on Fire” by Jaw 3:55] Status: Music Exchange Center (2 users on-line, 9 songs available) On-Line Users: [Ronnie Rocker: 4 songs (online), Peter Punk: 5 songs (online)] Available Songs: [“Rock is Cool” by Yeah 4:17, “My Girl is Mean to Me” by Can’t Stand Up 3:29, “Only You Can Rock Me” by UFO 4:52, “We’re Not Gonna Take It” by Twisted Sister 3:9, “Bite My Arms Off” by Jaw 4:12, “Where’s My Sweater” by The Knitters 3:41, “Is that My Toenail ?” by Clip 4:47, “Anvil Headache” by Clip 4:34, “My Hair is on Fire” by Jaw 3:55] Available Songs By Jaw: [“Bite My Arms Off” by Jaw 4:12, “My Hair is on Fire” by Jaw 3:55] Status: Music Exchange Center (0 users on-line, 0 songs available) On-Line Users: [] Available Songs: [] Available Songs By Jaw: [] (3) Downloading Music Go back to the Song class and add to it an attribute called owner which will be a User object representing the user who happens to own this copy of this song. Note that a Song object may only be owned by one User and that many users can have copies of the same song. Set it to null initially. In the User class, adjust the addSong(Song s) method so that it sets the owner properly. In the User class, add a method called requestCompleteSonglist(MusicExchangeCenter m). This method should gather the list of all available songs from all users that are online at the given music exchange center (i.e., the union of all of their local song lists), and then return an ArrayList formatted as follows (note: there should be 1 String element in the ArrayList per line): COMP 1006A/1406A – F18 – A4 Due Friday, March 20th at 11:59 PM 4 TITLE ARTIST TIME OWNER 1. Hey Jude The Beatles 4:35 Disco Stew 2. Barbie Girl Aqua 3:54 Disco Stew 3. Only You Can Rock Me UFO 4:59 Disco Stew 4. Paper Soup Cats Jaw 4:18 Disco Stew 5. Rock is Cool Yeah 4:17 Ronnie Rocker 6. My Girl is Mean to Me Can’t Stand Up 3:29 Ronnie Rocker 7. Only You Can Rock Me UFO 4:52 Ronnie Rocker 8. We’re Not Gonna Take It Twisted Sister 3:09 Ronnie Rocker Notice that the songs are numbered and that the title, artist, time and owner are all lined up nicely. You should use the String.format() method as described in the notes (Chapter 1). Recall that %-30s in the format string will allow you to display a leftjustified 30-character string. Also, %2d and %02d will allow you to display numbers so that they take 2 places, the 0 indicating that a leading zero character is desired. In the User class, add a method called requestSonglistByArtist(MusicExchangeCenter m, String artist). This method should gather the list of all available songs by the given artist from all users that are online at the given music exchange center (i.e., the union of all of their local song lists), and then return an ArrayList formatted similar to that shown above. In the MusicExchangeCenter class, add a method called getSong(String title, String ownerName) which returns the Song object with the given title owned by the user with the given ownerName, provided that the user is currently online and that the song exists. Return null otherwise. (Hint: you will need to search through the center’s users to find User with the matching ownerName and then search through that user’s songs to find the Song with the given title. It may be a good idea to write an extra helper method in the User class called songWithTitle(String title) that you can make use of). In the User class, add a downloadSong(MusicExchangeCenter m, String title, String ownerName) method that simulates the downloading of one of the songs in the catalog. It should use the getSong(String title, String ownerName) method that you just wrote, and add the downloaded song to the user’s songList (if not null). Download and execute the MusicExchangeTestProgram2.java file to test your new code. Here is the expected output: COMP 1006A/1406A – F18 – A4 Due Friday, March 20th at 11:59 PM 4 Status: Music Exchange Center (5 users on-line, 18 songs available) Complete Song List: TITLE ARTIST TIME OWNER 1. Hey Jude The Beatles 4:35 Disco Stew 2. Barbie Girl Aqua 3:54 Disco Stew 3. Only You Can Rock Me UFO 4:59 Disco Stew 4. Paper Soup Cats Jaw 4:18 Disco Stew 5. Rock is Cool Yeah 4:17 Ronnie Rocker 6. My Girl is Mean to Me Can’t Stand Up 3:29 Ronnie Rocker 7. Only You Can Rock Me UFO 4:52 Ronnie Rocker 8. We’re Not Gonna Take It Twisted Sister 3:09 Ronnie Rocker 9. Meadows Sleepfest 7:15 Sleeping Sam 10. Calm is Good Waterfall 6:22 Sleeping Sam 11. If I Had a Hammer Long Road 4:15 Country Candy 12. My Man is a 4×4 Driver Ms. Lonely 3:07 Country Candy 13. This Song is for Johnny Lone Wolf 4:22 Country Candy 14. Bite My Arms Off Jaw 4:12 Peter Punk 15. Where’s My Sweater The Knitters 3:41 Peter Punk 16. Is that My Toenail ? Clip 4:47 Peter Punk 17. Anvil Headache Clip 4:34 Peter Punk 18. My Hair is on Fire Jaw 3:55 Peter Punk Disco Stew before downloading: Disco Stew: 4 songs (online) Disco Stew after downloading: Disco Stew: 7 songs (online) Disco Stew after downloading Ronnie’s: Disco Stew: 8 songs (online) Song’s by Jaw: TITLE ARTIST TIME OWNER 1. Paper Soup Cats Jaw 4:18 Disco Stew 2. Bite My Arms Off Jaw 4:12 Disco Stew 3. Bite My Arms Off Jaw 4:12 Peter Punk 4. My Hair is on Fire Jaw 3:55 Peter Punk (4) Paying the Price Now, in order to make all of this legal, we must have a way to compensate the musical artists for their hard work and wonderful music. An artist should receive 25 cents each time one of their songs is downloaded. Hence, for each artist, we will keep track of how much money in royalties they have. Add the following attributes to the MusicExchangeCenter class: royalties – a HashMap with the artists’ names as the keys and the values are floats representing the total amount of royalties for that artist so far. It should only contain artists who have had songs downloaded. You will update this HashMap later. COMP 1006A/1406A – F18 – A4 Due Friday, March 20th at 11:59 PM 4 downloadedSongs – an ArrayList containing all of the songs that have been downloaded. This list will, in general, contain duplicate Song objects. Write a method in the MusicExchangeCenter class called displayRoyalties() that displays the royalties for all artists who have had at least one of their songs downloaded. It should display a two-line header and then one line per artist showing the royalty amount as well as the artist name as follows: Amount Artist ————— $0.75 Sleepfest $1.50 Clip $0.25 Jaw $0.50 Long Road $0.25 Yeah $0.25 UFO In the getSong() method in the MusicExchangeCenter, adjust the code so that if the song is found (i.e., able to be downloaded), then it is added to the downloadedSongs list. Additionally, the royalties for the artist of the song should be updated within this method. Write a method in the MusicExchangeCenter class called uniqueDownloads() that returns (i.e., not displays) a TreeSet of all downloaded Song objects such that the set is sorted alphabetically by song title. There should be no duplicates songs in this set. To add the Song objects to the TreeSet, the Song class will need to implement Comparable and you will need to write the corresponding compareTo(Song s) method in the Song class. Write a method in the MusicExchangeCenter class called songsByPopularity() that returns (i.e., not displays) an ArrayList of Pair<Integer,Song> objects where the key of the pair is an Integer representing the number of downloads and the value is the Song object. The integer key should represent the number of times that the song was downloaded. The list returned should be sorted in decreasing order according to the number of times the song was downloaded. To sort a list of Pair objects, you can use the following code: Collections.sort(yourListOfPairs, new Comparator<Pair<Integer, Song>>() { public int compare(Pair<Integer, Song> p1, Pair<Integer, Song> p2) { // PUT YOUR CODE IN HERE } }); COMP 1006A/1406A – F18 – A4 Due Friday, March 20th at 11:59 PM 4 Just insert the missing code so that it returns an appropriate integer indicating whether pair p1 comes before or after pair p2 in the sort order (see notes, Chapter 8, Page 281). Run the MusicExchangeTestProgram3.java test file to make sure it works with your code. Here is the expected output: Status: Music Exchange Center (5 users on-line, 18 songs available) Here are the downloaded songs: “Bite My Arms Off” by Jaw 4:12 “Meadows” by Sleepfest 7:15 “If I Had a Hammer” by Long Road 4:15 “Is that My Toenail ?” by Clip 4:47 “Anvil Headache” by Clip 4:34 “Is that My Toenail ?” by Clip 4:47 “If I Had a Hammer” by Long Road 4:15 “Anvil Headache” by Clip 4:34 “Meadows” by Sleepfest 7:15 “Only You Can Rock Me” by UFO 4:52 “Is that My Toenail ?” by Clip 4:47 “Is that My Toenail ?” by Clip 4:47 “Rock is Cool” by Yeah 4:17 “Meadows” by Sleepfest 7:15 Here are the unique downloaded songs alphabetically: “Anvil Headache” by Clip 4:34 “Bite My Arms Off” by Jaw 4:12 “If I Had a Hammer” by Long Road 4:15 “Is that My Toenail ?” by Clip 4:47 “Meadows” by Sleepfest 7:15 “Only You Can Rock Me” by UFO 4:52 “Rock is Cool” by Yeah 4:17 Here are the downloaded songs by populariry: (4 downloads) “Is that My Toenail ?” by Clip 4:47 (3 downloads) “Meadows” by Sleepfest 7:15 (2 downloads) “Anvil Headache” by Clip 4:34 (2 downloads) “If I Had a Hammer” by Long Road 4:15 (1 downloads) “Bite My Arms Off” by Jaw 4:12 (1 downloads) “Only You Can Rock Me” by UFO 4:52 (1 downloads) “Rock is Cool” by Yeah 4:17 Here are the royalties: Amount Artist ————— $0.75 Sleepfest $1.50 Clip COMP 1006A/1406A – F18 – A4 Due Friday, March 20th at 11:59 PM 4 $0.25 Jaw $0.50 Long Road $0.25 Yeah $0.25 UFO
