Question

我得到一个不寻常的，

NullPointerException: Exception in thread "main" java.lang.NullPointerException.

我自己的TeamClass：

  public DSALinkedList<String> players;
  private String name, contactName, ContactAddr, contactEmail, parent;

public Team(String inName, String inConName, String inConAddr, String inConEmail, String inParent)
{     


        name = inName;
        DSALinkedList<String> players = new DSALinkedList<String>(); //Constructs an empty players list using Strings as the value.
        parent = inParent;
        contactName = inConName;
        ContactAddr = inConAddr;
        contactEmail = inConEmail;

}

//使用方法

public void addPlayer(String inPlayer)
{
    players.insertFirst(inPlayer);        
}

然后在我的主课程中，我从文件构建一个团队，调用这个方法：

public static Team constructTeam(String inLine)
    {
   String[] lineArray = new String[16];
   lineArray = inLine.split(",");  

    int i;
    String name, contact, email, address, parent;
    name = lineArray[1];
    parent = lineArray[2];
    contact = lineArray[3];
    email = lineArray[4];
    address = lineArray[5];

    Team team = new Team(name, contact, address, email, parent);
    System.out.println(team.getName());

//这是一个完整性检查，这会正确打印团队名称，这对我来说显示了团队＆＃39;不是空的。
//将玩家（字符串）添加到玩家列表中。＆＃34; PLAYER：FirstName LastName＆＃34;

    for(i=6; i<15; i++) //First player in lineArray to potentially the last.
    {
        if(!lineArray[i].equals("")) 
        {
            System.out.println("Test:"+ lineArray[i]);
            String player = lineArray[i];
            team.addPlayer(player); //ERROR OCCURS HERE
        }
    }

  return team;
}

Answer 1

您正在构造函数DSALinkedList<String> players中的此行上重新声明您的类变量DSALinkedList<String> players = new DSALinkedList<String>();，

应该只有 - players = new DSALinkedList<String>();

因此，在下面的方法中，players因其类变量而为NULL。

public void addPlayer(String inPlayer) {
    players.insertFirst(inPlayer);        
}

Answer 2

将通过以下方式使用播放器：

public DSALinkedList<String> players;
  private String name, contactName, ContactAddr, contactEmail, parent;

public Team(String inName, String inConName, String inConAddr, String inConEmail, String inParent)
{     


        name = inName;
        players = new DSALinkedList<String>(); //Constructs an empty players list using Strings as the value.
        parent = inParent;
        contactName = inConName;
        ContactAddr = inConAddr;
        contactEmail = inConEmail;

}

链表的泛型中的异常NullPointerException

2 个答案: