當方法調用另一個方法時，ArrayList是否爲空？

我想調試pickPlayers。添加「選擇」後，列表「播放器」成功填充，但當調用「isPlaying」時，它爲空。當方法調用另一個方法時，ArrayList是否爲空？

任何人都可以看到爲什麼？我確保推入第一個元素，因此它實際上不應該是是 null數組列表;一旦完成並且「正在播放」，我就看不到它在哪裏排空球員。

public abstract class Game { 
protected ArrayList<Player> players; 

public Game(String gameName, int numPlayers) { 
    this.name = gameName; 
    this.totalPlayers = numPlayers; 
} 

public void pickPlayers(ArrayList<Player> players, int num){ 
    // rand int between 0 and number of players 
    Random generator = new Random(); 
    int rand = generator.nextInt(num) + 0; 

    Player choice = null;  
    int i = 0; 

    // first player 
    for (Player player: players){ 
     if (i == rand){ 
      choice = player; 
     } 
     i++; 
    } 
    players.add(choice); 
    i=1; 

    while (i < num){ 
     rand = generator.nextInt(num) + 0; 

     int a=0; 
     for (Player player: players){ 
      if (a == rand){ 
       choice = player; 
       System.out.println(choice.getName()); 
      } 
      a++; 
     } 

     if (!isPlaying(choice)){ 
      i++; 
      players.add(choice); 
      choice.play(); 
      System.out.println(choice.getName()); 
     } 
    } 
} 

public boolean isPlaying(Player p){ 
    return players.contains(p); 
} 
}

來源

2014-02-26 HB-