Измените вызов плейлиста, чтобы класс Album использовал внутренний класс.
Вместо того, чтобы использовать ArrayList для хранения треков, он будет использовать внутренний класс SongList.
Внутренний класс SongList будет использовать ArrayList и предоставит метод для добавления песни.
Он также предоставляет методы findSong(), которые будут использоваться содержащим классом Album для добавления песен в список воспроизведения.
Ни класс Song, ни класс Main не должны изменяться.
Альбом.java
package com.timbuchalka;import java.util.ArrayList; import java.util.LinkedList;/** * Created by dev on 18/09/15. */ public class Album { private String name; private String artist; private ArrayList<Song> songs;public Album(String name, String artist) { this.name = name; this.artist = artist; this.songs = new ArrayList<Song>(); }public boolean addSong(String title, double duration) { if(findSong(title) == null) { this.songs.add(new Song(title, duration)); return true; } return false; }private Song findSong(String title) { for(Song checkedSong: this.songs) { if(checkedSong.getTitle().equals(title)) { return checkedSong; } } return null; }public boolean addToPlayList(int trackNumber, LinkedList<Song> playList) { int index = trackNumber -1; if((index >0) && (index <= this.songs.size())) { playList.add(this.songs.get(index)); return true; } System.out.println("This album does not have a track " + trackNumber); return false; }public boolean addToPlayList(String title, LinkedList<Song> playList) { Song checkedSong = findSong(title); if(checkedSong != null) { playList.add(checkedSong); return true; } System.out.println("The song " + title + " is not in this album"); return false; }}
Песня.java
package com.timbuchalka;/** * Created by dev on 18/09/15. */ public class Song { private String title; private double duration;public Song(String title, double duration) { this.title = title; this.duration = duration; }public String getTitle() { return title; }@Override public String toString() { return this.title + ": " + this.duration; } }
Main.java
package com.timbuchalka;import java.util.*;public class Main {private static ArrayList<Album> albums = new ArrayList<Album>();public static void main(String[] args) { // Create a program that implements a playlist for songs // Create a Song class having Title and Duration for a song. // The program will have an Album class containing a list of songs. // The albums will be stored in an ArrayList // Songs from different albums can be added to the playlist and will appear in the list in the order // they are added. // Once the songs have been added to the playlist, create a menu of options to:- // Quit,Skip forward to the next song, skip backwards to a previous song. Replay the current song. // List the songs in the playlist // A song must exist in an album before it can be added to the playlist (so you can only play songs that // you own). // Hint: To replay a song, consider what happened when we went back and forth from a city before we // started tracking the direction we were going. // As an optional extra, provide an option to remove the current song from the playlist // (hint: listiterator.remove()Album album = new Album("Stormbringer", "Deep Purple"); album.addSong("Stormbringer", 4.6); album.addSong("Love don't mean a thing", 4.22); album.addSong("Holy man", 4.3); album.addSong("Hold on", 5.6); album.addSong("Lady double dealer", 3.21); album.addSong("You can't do it right", 6.23); album.addSong("High ball shooter", 4.27); album.addSong("The gypsy", 4.2); album.addSong("Soldier of fortune", 3.13); albums.add(album);album = new Album("For those about to rock", "AC/DC"); album.addSong("For those about to rock", 5.44); album.addSong("I put the finger on you", 3.25); album.addSong("Lets go", 3.45); album.addSong("Inject the venom", 3.33); album.addSong("Snowballed", 4.51); album.addSong("Evil walks", 3.45); album.addSong("C.O.D.", 5.25); album.addSong("Breaking the rules", 5.32); album.addSong("Night of the long knives", 5.12); albums.add(album);LinkedList<Song> playList = new LinkedList<Song>(); albums.get(0).addToPlayList("You can't do it right", playList); albums.get(0).addToPlayList("Holy man", playList); albums.get(0).addToPlayList("Speed king", playList); // Does not exist albums.get(0).addToPlayList(9, playList); albums.get(1).addToPlayList(8, playList); albums.get(1).addToPlayList(3, playList); albums.get(1).addToPlayList(2, playList); albums.get(1).addToPlayList(24, playList); // There is no track 24play(playList);}private static void play(LinkedList<Song> playList) { Scanner scanner = new Scanner(System.in); boolean quit = false; boolean forward = true; ListIterator<Song> listIterator = playList.listIterator(); if(playList.size() == 0) { System.out.println("No songs in playlist"); return; } else { System.out.println("Now playing " + listIterator.next().toString()); printMenu(); }while(!quit) { int action = scanner.nextInt(); scanner.nextLine();switch(action) { case 0: System.out.println("Playlist complete."); quit = true; break; case 1: if(!forward) { if(listIterator.hasNext()) { listIterator.next(); } forward = true; } if(listIterator.hasNext()) { System.out.println("Now playing " + listIterator.next().toString()); } else { System.out.println("We have reached the end of the playlist"); forward = false; } break;case 2: if(forward) { if(listIterator.hasPrevious()) { listIterator.previous(); } forward = false; } if(listIterator.hasPrevious()) { System.out.println("Now playing " + listIterator.previous().toString()); } else { System.out.println("We are at the start of the playlist"); forward = true; } break; case 3: if(forward) { if(listIterator.hasPrevious()) { System.out.println("Now replaying " + listIterator.previous().toString()); forward = false; } else { System.out.println("We are at the start of the list"); } } else { if(listIterator.hasNext()) { System.out.println("Now replaying " + listIterator.next().toString()); forward = true; } else { System.out.println("We have reached the end of the list"); } } break; case 4: printList(playList); break; case 5: printMenu(); break;case 6: if(playList.size() >0) { listIterator.remove(); if(listIterator.hasNext()) { System.out.println("Now playing " + listIterator.next()); } else if(listIterator.hasPrevious()) { System.out.println("Now playing " + listIterator.previous()); } } break;} } }private static void printMenu() { System.out.println("Available actions:\npress"); System.out.println("0 - to quit\n" + "1 - to play next song\n" + "2 - to play previous song\n" + "3 - to replay the current song\n" + "4 - list songs in the playlist\n" + "5 - print available actions.\n" + "6 - delete current song from playlist");}private static void printList(LinkedList<Song> playList) { Iterator<Song> iterator = playList.iterator(); System.out.println("================================"); while(iterator.hasNext()) { System.out.println(iterator.next()); } System.out.println("================================"); }}
解答參考：
Альбом.java
import java.util.ArrayList; import java.util.LinkedList;public class Album { private String name; private String artist; private SongList songs;public Album(String name, String artist) { this.name = name; this.artist = artist; this.songs = new SongList(); }public boolean addSong(String title, double duration) { return this.songs.add(new Song(title, duration)); }public boolean addToPlayList(int trackNumber, LinkedList<Song> playList) { Song checkSong = this.songs.findSong(trackNumber); if (checkSong != null) { playList.add(checkSong); return true; } System.out.println("This album does not have a track " + trackNumber); return false; }public boolean addToPlayList(String title, LinkedList<Song> playList) { Song checkedSong = this.songs.findSong(title); if (checkedSong != null) { playList.add(checkedSong); return true; } System.out.println("The song " + title + " is not in this album"); return false; }private class SongList {private ArrayList<Song> songs;private SongList() { this.songs = new ArrayList<Song>(); }private boolean add(Song song) { if (this.songs.contains(song)) { return false; } this.songs.add(song); return true; }private Song findSong(String title) { for (Song checkedSong : this.songs) { if (checkedSong.getTitle().equals(title)) { return checkedSong; } } return null; }private Song findSong(int trackNumber) { int index = trackNumber - 1; if ((index >= 0) && index < this.songs.size()) { return this.songs.get(index); } return null; } } }
