CODEWITHSUNDEEP
java
Patric Bernard
Patric Bernard

Reputation: 31

What is with these strange errors

I'm not sure what I am doing wrong here. I'm fairly new to Java programming.

My goal was to have 4 players enter their names and scores of a game, and then return the names and scores in descending order or scores.

I created a class, with a Player. And then made a dynamic variable to change how many objects I make.

I ask for the username, and then the score, but that's where I am getting stuck. The program compiles fine, but it tells me this. "What is the name of Player # 1?Exception in thread "main" java.lang.NullPointerException
at HelloWorld.main(HelloWorld.java:20)"

I'm not sure why I'm getting this error. Can anyone help me?

//Array
import java.util.*;

public class HelloWorld {
    public static void main(String[] args){

        Scanner input = new Scanner(System.in);
        int allPlayers;
        int index[] = new int[12];
        int i;
        System.out.print("Please enter the number of players");
        allPlayers = input.nextInt();

        Player[]  playersArray = new Player[allPlayers];

        for(i = 0; i <allPlayers; i++){
            System.out.print("What is the name of Player # " + (i+1) +"?");
            playersArray[i].name = input.nextLine();
            System.out.print("What was the score of Player # " + (i+1) + "?");
            playersArray[i].score = input.nextInt();
         }

         for(i = 0; i <allPlayers; i++){
             for(int j = 0; j <allPlayers; j++){
                 if(index[i] < playersArray[j].score){
                     index[i] = playersArray[j].score;
                 }
              }
          }
          for(i = 0; i <allPlayers; i++){
              System.out.print(playersArray[index[i]].name);
              System.out.print(playersArray[index[i]].score);
          }
    }
}
class Player {
    int score;    // players score 
    String name;  // players name
}

Upvotes: 0

Views: 43

Answers (2)

Danyal Sandeelo
Danyal Sandeelo

Reputation: 12391

You are declaring it but not assigning the memory to the object, that's why getting a NULL Pointer exception. Right before assigning the values, create the object.

for(i = 0; i <allPlayers; i++){
            playersArray[i] = new Player();

Upvotes: 0

Eran
Eran

Reputation: 393771

When you initialize an array of reference type :

Player[]  playersArray = new Player[allPlayers];

all the elements of the array are initialized to null.

You forgot to initialize playersArray[i].

Add 

playersArray[i] = new Player();

before

playersArray[i].name = ...

Upvotes: 2

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