Java Create array out of parameter in object creation

Question

I'm trying to make a simple game in Java. In my main class, I let the player type in their names and how many players will be playing.

here is my code in the main class:

{...}
Board game = new Board (playerNames,numberOfPlayers);
        game.run();
{...}

Now in my other class it looks like this:

    private int numberOfPlayers;
    private Player[] players = new Player[numberOfPlayers];
    private String[] playerNames= new String[numberOfPlayers];
    private PlayerHand[] hands = new PlayerHand[numberOfPlayers];

public Board(String[] s, int n) {   
        playerNames=s;
        numberOfPlayers= n;
    }

it then initializes the Players like this:

public  void initializePlayer(){    
        for(int i=0;i<numberOfPlayers;i++){
            hands[i]=new PlayerHand();
            players[i]=new Player(playerNames[i],hands[i]);}

For testing I always set the numberOfPlayers directly in the Board class. Since I want to change it now that the ammount of players is not fixed anymore, I have a problem. I assume the problem is that the Arrays get initialized with 0, as numberOfPlayers is 0 at the beginning. How can I change this?

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0

Eran · Accepted Answer · 2016-12-01 13:54:31Z

3

You instantiate the arrays while numberOfPlayers still contains its default value of 0, so they are all empty arrays.

You should instantiate them in the constructor.

public Board(String[] s, int n) {   
    playerNames=s;
    numberOfPlayers= n;
    players = new Player[numberOfPlayers];
    playerNames= new String[numberOfPlayers];
    hands = new PlayerHand[numberOfPlayers];
}

answered Dec 1, 2016 at 13:54

Eran

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5 Comments

Allantir Over a year ago

ok, i did this, but the Player has to be instantiated with name and hands. i tried it with for (int i = 0; i < numberOfPlayers; i++) { players[i]=new Player(playerNames[i],hands[i]); } But i'm getting a NullPointerException now.

Eran Over a year ago

@Allantir You should probably initialize playerNames[i] and hands[i] before initializing players[i].

Allantir Over a year ago

it looks now like this:

players = new Player[numberOfPlayers]; 		hands = new PlayerHand[players.length]; 		for (int i = 0; i < players.length; i++) { 			players[i]=new Player(playerNames[i],hands[i],);

should i initialize them differently?

Eran Over a year ago

@Allantir Where do you initialize playerNames[i] and hands[i]?

Allantir Over a year ago

nvm, i got it now, i instatiate them now in the constructor hands = new PlayerHand[numberOfPlayers]; and then run through the for Loop hands[i] = new PlayerHand(); the code works now! Am i doing anything unnecessary in it? it seems rather long. Other than that, thank you very much for the help

ItamarG3 · Accepted Answer · 2016-12-01 13:56:07Z

1

When you create the arrays, their sizes are 0 because numOfPlayers is 0 at that point.
You need to create initialize them in the constructor after you assign the player number a value

private int numberOfPlayers; 
private Player[] players;
private String[] playerNames;
private PlayerHand[] hands;
public Board(String[] s, int n) { 
    playerNames=s; 
    numberOfPlayers= n; 
    players = new Player[numberOfPlayers]; 
    playerNames= new String[numberOfPlayers]; 
     hands = new PlayerHand[numberOfPlayers];
}

answered Dec 1, 2016 at 13:56

ItamarG3

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Comments

Andrew · Accepted Answer · 2016-12-01 14:01:38Z

1

The line

private String[] playerNames = new String[numberOfPlayers];

equals to

private String[] playerNames = new String[0];

because an instance field is initialized with a default value (0 for int).

You should move all initialization stuff to a controller where a size of arrays will be known. Furthermore, there is no need to keep a number of players (n) after array initialization (players.length will return the same):

public Board(String[] s, int n) {
    ...
    players = new Player[n];
}

edited Dec 1, 2016 at 14:01

answered Dec 1, 2016 at 13:55

Andrew

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1 Comment

Allantir Over a year ago

that is probably the prettiest solution and i will do that

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