將對象從一個類移動到另一個類（Java）

Question

只是想知道如何創建歌曲對象（歌曲1，歌曲2，歌曲3，歌曲4）的播放列表，其中每個對象都有自己的值（名稱，藝術家，文件大小，持續時間）。我無法爲這個程序使用數組/列表。只要看看下面的getSong()和addSongToPlaylist()方法，我包括其他方法只是爲了顯示歌曲對象的結構。

這是我SongDatabase類：

public class SongDatabase { 
    Scanner console = new Scanner(System.in); 
    private Song song1=null, song2=null, song3=null, song4=null; 

public void addNewSong() {   
    if (song1 == null) { 
     song1 = getFromUser(); 
    } 
    else if (song2 == null) { 
     song2 = getFromUser(); 
    }  
    else if (song3 == null) { 
     song3 = getFromUser(); 
    } 
    else if (song4 == null) { 
     song4 = getFromUser(); 
    } 
    else { 
     System.out.println("The database is currently full. Please delete a song before adding a new one."); 
     System.out.println(""); 
    }  
} 

private Song getFromUser() { 
    Song song = new Song(); 

    System.out.println("Name of song:"); 
    song.setName(console.next()); 

    System.out.println("Artist:"); 
    song.setArtist(console.next()); 

    System.out.println("File size (MB):"); 
    song.setFileSize(console.nextInt()); 

    System.out.println("Duration (seconds):"); 
    song.setDuration(console.nextInt()); 

    System.out.println("Song successfully added.");/
    System.out.println(""); 

    return song; 
} 

public Song getSong(int songNumber) { 
    if (songNumber == 1){ 
     return song1; 
    } 
    else if (songNumber == 2){ 
     return song2; 
    } 
    else if (songNumber == 3){ 
     return song3; 
    } 
    else if (songNumber == 4){ 
     return song4; 
    } 

    else { 
     return song1; 
    } 
} 

然後我的菜單類：

public class Menu { 

    Scanner console = new Scanner(System.in); 
    private SongDatabase database = new SongDatabase(); 
    private Playlist playlist = new Playlist(); 
    private int songCount=0; 

private void addSongToPlaylist() { 
    if (songCount <=3) { 

    System.out.println("Please enter the number of the song you'd like to be added to the playlist."); 
    System.out.println(""); 

    int songNumber; 
    songNumber = console.nextInt(); 

    switch (songNumber) { 
     case 1: 
      playlist.setSong(database.getSong(1)); 
      break; 
     case 2: 
      playlist.setSong(database.getSong(2)); 
      break; 
     case 3: 
      playlist.setSong(database.getSong(3)); 
      break; 
     case 4: 
      playlist.setSong(database.getSong(4)); 
      break; 
     default: 
      System.out.println("Please enter a valid song number."); 
      break; 
    } 
    songCount++; 
    } 

到目前爲止，addSongToPlaylist()方法應該從getSong()法權鬆1對象？但我不確定如何將這些歌曲對象添加到Playlist類中的播放列表中。我知道我需要像public void setSong(parameters?)這樣的方法，但我不確定如何構造它。有任何想法嗎？幫助將不勝感激，謝謝！

Answer 1

如果您不能使用List或Array，如果你PlayList限制爲3 Songs那麼你可以嘗試這樣的

public class Playlist { 
    private Song firstSong; 
    private Song secondSong; 
    private Song thirdSong; 

    public void setSong(Song song) { 
     if (song != null) { 
      if (firstSong == null) { 
       firstSong = song; 
      } else if (secondSong == null) { 
       secondSong = song; 
      } else if (thirdSong == null) { 
       thirdSong = song; 
      } 
     } 
    } 
} 

Answer 2

可以使用任何數據結構保持的歌曲列表，狀陣列，列表，組，映射等等下面

是使用列表的示例的代碼。

class PlayList { 
List<Song> songList = new ArrayList<Song>(); 

void addSongInList(Song song){ 
    songList.add(song)l 
} 

}