Mehran Sahami Handout #43 CS 106A November 28, 2007

Mehran Sahami Handout #43 CS 106A November 28, 2007 FlyTunes Program (Data Structures Example) File: Song.java /* * File: Song.java * --------------- * Keeps track of the information for one song * in the music shop, including its name, the band * that it is by, and its price. */ public class Song { /** Constructor * Note that the song name and band name are immutable * once the song is created. */ public Song(String songName, String bandName, double songPrice) { title = songName; band = bandName; price = songPrice; } public String getSongName() { return title; } public String getBandName() { return band; } public void setPrice(double songPrice) { price = songPrice; } public double getPrice() { return price; } /** Returns a string representation of a song, listing * the song name, the band name, and its price. */ public String toString() { return ("\"" + title + "\" by " + band + " costs $" + price); } /* private instance variables */ private String title; private String band; private double price; }
– 2 –
File: Album.java /* * File: Album.java * ---------------- * Keeps track of all the information for one album * in the music shop, including its name, the band that * its by, and the list of songs it contains. */ import java.util.*; public class Album { /** Constructor * Note that the album name and band name are immutable * once the album is created. */ public Album(String albumName, String bandName) { title = albumName; band = bandName; } public String getAlbumName() { return title; } public String getBandName() { return band; } /** Adds a song to this album. There is no duplicate * checking for songs that are added. */ public void addSong(Song song) { songs.add(song); } /** Returns an iterator over all the songs that are * on this album. */ public Iterator<Song> getSongs() { return songs.iterator(); } /** Returns a string representation of an album, listing * the album name and the band name. */ public String toString() { return ("\"" + title + "\" by " + band); } /* private instance variables */ private String title; private String band; private ArrayList<Song> songs = new ArrayList<Song>(); }
– 3 –
File: FlyTunesStore.java /* * File: FlyTunesStore.java
* ------------------------ * This program handles the data management for an on-line music store * where we manage an inventory of albums as well as individual songs. */ import acm.program.*; import java.util.*; public class FlyTunesStore extends ConsoleProgram { public void run() { while (true) { int selection = getSelection(); if (selection == QUIT) break; switch (selection) { case LIST_SONGS: listSongs(); break; case LIST_ALBUMS: listAlbums(); break; case ADD_SONG: addSong(); break; case ADD_ALBUM: addAlbum(); break; case LIST_SONGS_ON_ALBUM: listSongsOnAlbum(); break; case UPDATE_SONG_PRICE: updateSongPrice(); break; default: println("Invalid selection"); break; } } } /** Prompts the user to pick a selection from a menu * of options. Returns the users selection. Note that * there is no bounds checking done on the users selection. */ private int getSelection() { println(); println("Please make a selection (0 to quit):"); println("1. List all songs"); println("2. List all albums"); println("3. Add a song"); println("4. Add an album"); println("5. List songs on an album"); println("6. Update song price"); int choice = readInt("Selection: "); return choice; }
– 4 –
/** Lists all the songs carried by the store */ private void listSongs() { println("All songs carried by the store:"); for(int i = 0; i < songs.size(); i++) { println(songs.get(i).toString()); } } /** Lists all the albums carried by the store */ private void listAlbums() { println("All albums carried by the store:"); Iterator<String> albumIt = albums.keySet().iterator(); while (albumIt.hasNext()) { println(albums.get(albumIt.next()).toString()); } } /** Checks to see if the song (defined by its name and * the band that performs it) is already in the store. It * returns the index of the song in the store's song list * if it already exists and -1 otherwise. */ private int findSong(String name, String band) { int index = -1; for(int i = 0; i < songs.size(); i++) { if (songs.get(i).getSongName().equals(name) && songs.get(i).getBandName().equals(band)) { index = i; break; // don't need to finish the loop } } return index; } /** Adds a new song to the store's inventory and returns that * song to the caller. If the song already exists in the * store, it returns the existing song from the inventory. * Otherwise it returns the new song that was just added to * the inventory. The method may return null if the user * decides not to enter a song (i.e., user just presses * Enter when asked for the song name). */ private Song addSong() { String name = readLine("Song name (Enter to quit): "); if (name.equals("")) return null; String band = readLine("Band name: "); int songIndex = findSong(name, band); if (songIndex != -1) { println("That song is already in the store."); return songs.get(songIndex); } else { double price = readDouble("Price: "); Song song = new Song(name, band, price); songs.add(song); println("New song added to the store."); return song; } }
– 5 –
/** Adds a new album to the store's inventory. If the album * already exists in the store, then the inventory is * unchanged. Otherwise a new album and any new songs it * contains are added to the store's inventory. */ private void addAlbum() { String name = readLine("Album name: "); if (albums.containsKey(name)) { println("That album is already in the store."); } else { String band = readLine("Band name: "); Album album = new Album(name, band); albums.put(name, album); while (true) { Song song = addSong(); if (song == null) break; album.addSong(song); } println("New album added to the store."); } } /** Lists all the songs on a single album in the inventory. */ private void listSongsOnAlbum() { String name = readLine("Album name: "); if (albums.containsKey(name)) { Iterator<Song> it = albums.get(name).getSongs(); println(name + " contains the following songs:"); while (it.hasNext()) { Song song = it.next(); println(song.toString()); } } else { println("No album by that name in the store."); } } /** Updates the price of a song in the store's inventory. * Note that this price update will also affect all albums * that contain this song. */ private void updateSongPrice() { String name = readLine("Song name: "); String band = readLine("Band name: "); int songIndex = findSong(name, band); if (songIndex == -1) { println("That song is not in the store."); } else { double price = readDouble("New price: "); songs.get(songIndex).setPrice(price); println("Price for " + name + " updated."); } }
– 6 –
/* Constants */ private static final int QUIT = 0; private static final int LIST_SONGS = 1; private static final int LIST_ALBUMS = 2; private static final int ADD_SONG = 3; private static final int ADD_ALBUM = 4; private static final int LIST_SONGS_ON_ALBUM = 5; private static final int UPDATE_SONG_PRICE = 6; /* Private instance variables */ // Inventory all the albums carried by the store private HashMap<String,Album> albums = new HashMap<String,Album>(); // Inventory of all the songs carried by the store private ArrayList<Song> songs = new ArrayList<Song>(); }