How to check the duplicate object in the array

Question

I am a java beginner and I am designing a Nim game for many players to join. I've done some research but I don't know if my implementation is correct. The aim is to check the duplicate object in an array. I've already checked some articles, and I'll reference them in the last part of this article.

For the NimPlayer class. I've created some things.

1. I've defined the NimPlayer object type.
2. Using the type, I can initialize the player in the limited space.

3. I initialize an array for saving player's data by following the steps here: Storing object into an array - Java

   public class NimPlayer {
   String userName;
   String familyName;
   String givenName;
   NimPlayer [] playerList = new NimPlayer[10]; //set an array here
   int id;
   
   //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 void createPlayer(String userName, String familyName, String givenName) {   
       playerList[id++] = new NimPlayer(userName, familyName, givenName);
   }
   

In the main method, I have created some features for players to use:

1. addplayer - let the user can add players in the game to compete.

2. To add the player, the Syntax like this:

   $addplayer userName,familyName,givenName
   

3. to validate the input, I split the input and store them in the new object.

   public static String[] splitName(String inputName) {
   String [] splittedLine = inputName.split(",");
   String userName = splittedLine[0].trim();
   String familyName = splittedLine[1].trim();
   String givenName = splittedLine[2].trim();
   String [] name = new String[3];
   name[0] = userName;
   name[1] = familyName;
   name[2] = givenName;
   return name;
   }
   
   public static void main(String[] args) {
   Scanner in = new Scanner(System.in);
   
   //create new object to save data
   NimPlayer playerData = new NimPlayer(null, null, null);
   
   System.out.print('$');
   String commandInput = in.next();
   
   while (true) {
   
       if (commandInput.equals("addplayer")) {
           String inputName = in.nextLine();
           String[] name = splitName(inputName);
           String userName = name[0];
           String familyName = name [1];
           String givenName = name[2];
   
           playerData.createPlayer(userName, familyName, givenName);
   
           for (int i = 0; i < playerData.playerList.length; i++) {
               NimPlayer player = playerData.playerList[i];
               System.out.println(player.getUserName()); }
   }
   

   So far, I have two questions here.

4. Every time I enter a set of data, it seems my "playerData" provokes the NullPointerException when looping through the object, but since my name input is multiple, I have to create a new object in the main method for saving input.

5. For checking if there is the duplicate "userName" in the set of the "inputName", I loop through the objects in an array. How can I access the "userName" in this situation?

for checking duplicate, I've checked:

1. Java - Loop through instances of a class rather than calling a method for each separate instance
2. What is a NullPointerException, and how do I fix it?
3. Java Array, Finding Duplicates

Answer 1

You should address then following things in your design/code:

1. Since you are creating a player using createPlayer(String userName, String familyName, String givenName), you should make the constructor, NimPlayer(String userName,String surName, String givenName) private so that it can not be called from outside of the class, NimPlayer. Also, declare createPlayer as static so that it doesn't need a NimPlayer object to be called on.
2. You need to have a static counter to keep track of the number of players and check the value of this counter before adding a new player to playerList.
3. You should also check the size of the resulting array after inputName.split(","). Similarly, you should check the size of the returned array from splitName before you access any element from it.

Given below is the code incorporating the points mentioned above:

import java.util.Scanner;

class NimPlayer {
    private String userName;
    private String familyName;
    private String givenName;
    //...
    // public getters and setters of userName, familyName, and givenName
    //...
    private static int counter = 0;
    private static NimPlayer[] playerList = new NimPlayer[10];

    private NimPlayer(String userName, String familyName, String givenName) {
        this.userName = userName;
        this.familyName = familyName;
        this.givenName = givenName;
    }

    public static void createPlayer(String userName, String familyName, String givenName) {
        if (counter < 10) {
            playerList[counter++] = new NimPlayer(userName, familyName, givenName);
        } else {
            System.out.println("The list is full.");
        }
    }

    public static int getCounter() {
        return counter;
    }

    public static NimPlayer[] getPlayers() {
        return playerList;
    }
}

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (true) {
            System.out.print('$');
            String commandInput = in.next();
            if (commandInput.equals("addplayer")) {
                String inputName = in.nextLine();
                String[] name = splitName(inputName);
                if (name != null && name.length == 3) {
                    NimPlayer.createPlayer(name[0], name[1], name[2]);
                }
            } else {
                break;
            }
        }
        for (int i = 0; i < NimPlayer.getCounter(); i++) {
            System.out.println(NimPlayer.getPlayers()[i].getUserName());
        }
    }

    public static String[] splitName(String inputName) {
        String[] splittedLine = inputName.split(",");
        String[] name = null;
        if (splittedLine.length == 3) {
            String userName = splittedLine[0].trim();
            String familyName = splittedLine[1].trim();
            String givenName = splittedLine[2].trim();
            name = new String[3];
            name[0] = userName;
            name[1] = familyName;
            name[2] = givenName;
        }
        return name;
    }
}

I didn't understand your another question:

For checking if there is the duplicate "userName" in the set of the "inputName", I loop through the objects in an array. How can I access the "userName" in this situation?