CODEWITHSUNDEEP
javanullpointerexceptioninstance-variables
user2252460
user2252460

Reputation: 3

How to properly use a for loop with object instances - I keep getting null pointer exception (Java)

I'm still learning the basics of Java so please bear with me. I'm creating a simple soccer simulator game, right now I'm trying to populate the game with players from different countries.

I've created a for loop to go through an array of the instantiated object for players but I keep getting a null pointer exception. Here is my code:

public static void main(String[] args) {

        SoccerPlayers[] newPlayer = new SoccerPlayers[5];
        for (int i = 0; i < newPlayer.length; i++){
            newPlayer[i].PlayerCountry();
            newPlayer[i].PlayerPosition();
            newPlayer[i].PlayerName();
            newPlayer[i].PlayerAge();
            newPlayer[i].PrintSoccerPlayer();
        }

    }

I don't know if it's the way I did my for loop or the way the other class handles the method since it's pointing to the first method used. Here is a sample of the method from the other class.

public class SoccerPlayers extends SoccerMain {

    public String playerContinent = "";
    public String playerPosition = "";
    public String playerCountry = "";
    public String playerFirstName = "";
    public String playerLastName = "";
    public String playerName = "";
    public int playerAge = 0;

    public void PlayerCountry(){

        int continent = randomNum.nextInt(6) + 1;
        int country = 0;

        if (continent == 1){
            playerContinent = "North America";
        }else if (continent == 2){
            playerContinent = "South America";
        }else if (continent == 3){
            playerContinent = "Europe";
        }else if (continent == 4){
            playerContinent = "Africa";
        }else if (continent == 5){
            playerContinent = "Asia";
        }else{
            playerContinent = "Oceanica";
        }

        if (playerContinent == "North America"){
            country = randomNum.nextInt(100) + 1;
            if (country > 0 && country < 11){
                playerCountry = "Canada";

Upvotes: 0

Views: 91

Answers (2)

Kakarot
Kakarot

Reputation: 4252

When creating an array of objects, the elements of the array are assigned default values i.e null. (dont get confused with arrays of array of primitives. for eg: in case of primitve int the default values would be 0).

Case 1: Array of Objects

   SoccerPlayers[] newPlayer = new SoccerPlayers[5];
   // now all elements of newPlayer are null
   System.out.println(newPlayer[0]); // prints null

Case 2 : Array of primitives

   int[] intArr = new int[5];
   // now all elements are initialized to 0 (default value for primitive int)
   System.out.println(intArr[0]); // prints 0

So you have to create new objects and store them in the array as per your need.

Change this : 

 for (int i = 0; i < newPlayer.length; i++){
         // create objects of SoccerPlayers and store them in array
         newPlayer[i] = new SoccerPlayers(); 
         newPlayer[i].PlayerCountry();
         .........
         .........

Upvotes: 3

APT
APT

Reputation: 365

Your initialization of the array just creates an array of 5 nulls. you need to populate the list before you can iterate over it.

Upvotes: 1

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