CODEWITHSUNDEEP
java
TerraNova993
TerraNova993

Reputation: 53

java.lang.NullPointerException when filling an array of objects

There's something I'm missing here. with this code I get a java.lang.NullPointerException:

public static void main(String[] args) {

    Board board = new Board();
    board.Initialise();

}


public class Board {

private Obj[][] tableau;

public void Board() {

    tableau = new Obj[8][8];    
}

public void Fill_Board() {

    tableau[0][0]= new Obj('B');
    }
}

But with this other code I get no error. What I am doing wrong, and how to initialize properly this array of object?

public class Board {

private Obj[][] tableau = new Obj[8][8];

public void Board() {

}

public void Fill_Board() {

    tableau[0][0]= new Obj('B');
    }
}

Upvotes: 0

Views: 600

Answers (2)

NPE
NPE

Reputation: 500257

Board() ends up being a member function and not a constructor, and therefore never gets called. The problem is the void keyword, which needs to be removed:

public Board() { /* removed the `void' */
    tableau = new Obj[8][8];    
}

Upvotes: 2

Austin Heerwagen
Austin Heerwagen

Reputation: 663

I get no error when I run this code (changing Obj to an actual class), perhaps you can provide a more concrete example with a main method of what you're trying to do?

If you're looking at making a constructor then it needs to be the same name as your class, i.e. Tab and have no return type.

So you would need to add:

public Tab() {
    // initialization code here
}

You're constructor will run whenever you create a new instance of that class. You want to use it to initialize all of your variables.

Tab t = new Tab(); // Constructor runs

Edit:

You're main method uses class Board but you have given us a class called Tab. I can assume that you really want class Board so you should change all Tab to Board in the above example, if that's what you're looking for.

Upvotes: 0

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