TableService类setNextPlayerCurrent方法测试异常排查

在TableService类中实现了切换当前玩家的setNextPlayerCurrent方法，但调用该方法时抛出java.util.NoSuchElementException: No value present异常。

TableService类相关代码 #

private ArrayList<Player> players = new ArrayList<>();
private Optional<Player> currentPlayer = Optional.empty();        

public void setNextPlayerCurrent() {
    int currentPlayerIndex = players.indexOf(currentPlayer.get());
    if (!lastPlayerCheck(currentPlayerIndex)) {
        currentPlayer = Optional.of(players.get(currentPlayerIndex + 1));
    }
    else {
        currentPlayer = Optional.of(players.get(0));
    }
}

public boolean lastPlayerCheck(int currentPlayerIndex) {
    if (currentPlayerIndex == (players.size() - 1)) {
        return true;
    }
    return false;
}

测试代码 #

@Test
void checkCurrentPlayerSetting() {
    List<Player> players = tableService.getPlayers();
    Optional<Player> currentPlayer = tableService.getCurrentPlayer();
    Player player1 = new Player("A", "Adam", 100);
    Player player2 = new Player("B", "Bella", 100);
    players.add(player1);
    players.add(player2);
    currentPlayer = Optional.of(players.get(0));

    int player1Index = players.indexOf(player1);
    int player2Index = players.indexOf(player2);
    System.out.println(player1Index); // 输出0
    System.out.println(player2Index); // 输出1
    System.out.println(players.indexOf(currentPlayer.get())); // 输出0

    tableService.setNextPlayerCurrent(); // 抛出异常

    //assertEquals(player2.getId(), currentPlayer.get().getId());
}

问题根源 #

测试代码中仅对**局部变量currentPlayer**赋值，并未修改TableService类内部的成员变量currentPlayer。调用setNextPlayerCurrent时，类内的currentPlayer仍为初始的Optional.empty()，执行currentPlayer.get()自然触发空值异常。

修复步骤 #

1. 给TableService添加设置当前玩家的方法
   在TableService类中新增方法，用于修改内部的currentPlayer成员变量：

   public void setCurrentPlayer(Optional<Player> currentPlayer) {
       this.currentPlayer = currentPlayer;
   }
   

2. 修改测试代码，正确设置类内的当前玩家
   将测试中给局部变量赋值的逻辑，替换为调用新增的setCurrentPlayer方法：

   @Test
   void checkCurrentPlayerSetting() {
       List<Player> players = tableService.getPlayers();
       Player player1 = new Player("A", "Adam", 100);
       Player player2 = new Player("B", "Bella", 100);
       players.add(player1);
       players.add(player2);
       // 调用新增方法，设置TableService内部的currentPlayer
       tableService.setCurrentPlayer(Optional.of(players.get(0)));
   
       int player1Index = players.indexOf(player1);
       int player2Index = players.indexOf(player2);
       System.out.println(player1Index); // 输出0
       System.out.println(player2Index); // 输出1
       System.out.println(players.indexOf(tableService.getCurrentPlayer().get())); // 输出0
   
       tableService.setNextPlayerCurrent(); // 不再抛出异常
   
       assertEquals(player2.getId(), tableService.getCurrentPlayer().get().getId());
   }
   

3. 额外优化（可选）
   为避免后续出现同类问题，可在setNextPlayerCurrent方法中先判断currentPlayer是否有值：

   public void setNextPlayerCurrent() {
       if (currentPlayer.isEmpty()) {
           // 可抛出自定义异常或设置默认玩家，根据业务需求处理
           throw new IllegalStateException("当前玩家未初始化");
       }
       int currentPlayerIndex = players.indexOf(currentPlayer.get());
       if (!lastPlayerCheck(currentPlayerIndex)) {
           currentPlayer = Optional.of(players.get(currentPlayerIndex + 1));
       } else {
           currentPlayer = Optional.of(players.get(0));
       }
   }
   

内容的提问来源于stack exchange，提问作者djasyfuj