java - 迭代时如何处理数组中的 null

Question

我正在处理一个经典的 Nim 游戏项目。对我来说，障碍是“仅”使用数组将玩家保存在对象数组中，这意味着在测试时我总是会遇到 NullPointerException 。而且我查遍了几乎所有的资料都没有这样的方法来处理这个问题。

处理它的一种方法是添加 if arr[i] != null 用于在迭代时检查 non-null 对象，但是随后，我需要编写它适用于我创建的每个方法。有没有办法只传递要检查的非空数组？

这是我的代码的一部分Nimsys:

public static void main(String[] args) {
    System.out.println("Welcome to Nim\n");
    Scanner in = new Scanner(System.in);
    while (true) {
        System.out.print('$');
        String commandin = in.next();

        if (commandin.equals("addplayer")) {
            String inputName = in.nextLine();
            String[] name = splitName(inputName);
            addPlayer(name);
        }

        if (commandin.equals("removeplayer")) {
            String user = in.nextLine().trim();

            if (user.equals("")) {
                System.out.println("Are you sure you want to remove all players? (y/n) \n");

                commandin = in.next();
                if (commandin.equals("y")) {
                    for (int i = 0; i < NimPlayer.getCounter(); i++) {
                        NimPlayer.getPlayer()[i] = null;
                    }
                    System.out.println("Remove all the players");
                }
            }
            if (!user.equals("")) {
                searchAndRemovePlayer(user);
            }
        }
 public static void searchAndRemovePlayer(String user) {
    for (int i = 0; i < NimPlayer.getCounter(); i++) {
        String userName = NimPlayer.getPlayer()[i].getUserName().trim();
        if (userName.equals(user)) {
            NimPlayer.getPlayer()[i] = null;
            System.out.println("Remove successfully!\n");// A test to see if the code runs
            return;
        }
    }
    System.out.println("The player does not exist.\n");
}
}

下面是我的 NimPlayer 类的一部分。

//username, given name, family name, number of game played, number of games won
public class NimPlayer {
private String userName;
private String familyName;
private String givenName;
private int score;
private int gamePlayed;

private static int counter;
private static final int SIZE = 5;
static NimPlayer[] playerList = new NimPlayer[SIZE]; // set an array here

//define NimPlayer data type
public NimPlayer(String userName, String surName, String givenName) {
    this.userName = userName;
    this.familyName = surName;
    this.givenName = givenName;

}
// create new data using NimPlayer data type
public static void createPlayer(String userName, String familyName, String givenName) {
    if (counter<SIZE) {
        playerList[counter++] = new NimPlayer(userName, familyName, givenName);
    } else {
        System.out.println("Cannot add more players.");
    }
}
public static int getCounter() {
    return counter;
}
public static NimPlayer [] getPlayer() {
    return playerList;
}

//getters and setters

}

Answer 1

您可以执行以下操作，

public static void searchAndRemovePlayer(String user) {
    NimPlayer[] players = Arrays.stream(NimPlayer.getPlayer())
                                .filter(Objects::nonNull)
                                .toArray(NimPlayer[]::new);
    for (int i = 0; i < players.length; i++) {  // replaced NimPlayer.getCounter() to avoid Index Out of Bound
        String userName = players[i].getUserName().trim();
        if (userName.equals(user)) {
            players[i] = null;
            System.out.println("Remove successfully!\n");// A test to see if the code runs
            return;
        }
    }
    System.out.println("The player does not exist.\n");
}

请注意，NimPlayer.getCounter() 已替换为 arr 长度，以避免 ArrayIndexOutOfBoundsException

更新:您可以在 getPlayer()

中添加逻辑

 public static NimPlayer [] getPlayer() {
    NimPlayer[] nimPlayers = Arrays.stream(playerList)
            .filter(Objects::nonNull)
            .toArray(NimPlayer[]::new);
    counter = nimPlayers.length;  //update the counter
    return nimPlayers;
}