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I'm writing this code where I'm calling a method to act on an element in an array of objects, and to do this I first need to check if the element is null. I am doing this using if(array[x][y]!=null), but I get a NPE pointing to this line and I don't understand why.

Here's the code in question:

Method to check:

    public void addPiece(Piece p, int x, int y){//Method to add a piece to a given space on the board

    if(gboard[x][y]!=null)//Check to see if space is empty before adding piece

        System.out.println("Error: Board space already occupied. Please choose another space.");

    else{

        gboard[x][y]=p;

        gboard[x][y].setXpos(x);

        gboard[x][y].setYpos(y);

    }
}

Main method where it is being called:

    public class PracticeMoves {//Demo method

public static void main(String[] args) {


    Scanner kb=new Scanner(System.in);

    Board board=new Board();

    Piece p1=new Piece("Droid","Blue", 0, 0);

    board.addPiece(p1,3,5);

Class where gboard is created:

    public class Board {

private Piece[][] gboard;//initialize a 2D array of Piece objects to form the gameboard

public Board() {//no-args constructor to initialize gboard

    Piece[][] gboard=new Piece[8][8];   
}

Class for the piece object:

    public class Piece {//abstract class that the rest of the pieces inherit from
private String name;
private String colour;
private int xpos;
private int ypos;
public Piece(String n, String c, int x, int y){
    name=n;
    colour=c;
    xpos=x;
    ypos=y;
}
public String getName() {//getter and setter methods
    return name;
}
public void setName(String name) {
    this.name = name;
}
public String getColour() {
    return colour;
}
public void setColour(String colour) {
    this.colour = colour;
}
public int getXpos() {
    return xpos;
}
public void setXpos(int xpos) {
    this.xpos = xpos;
}
public int getYpos() {
    return ypos;
}
public void setYpos(int ypos) {
    this.ypos = ypos;
}
public String toString() {//toString method
    return name+colour;
}

}

Any help would be much appreciated. If there is any other part of the code you might need to see please let me know.

Thanks.

EDIT: Since this is being marked as a duplicate, I want to point out the the question I was referred to is asking what a NPE is. I know what it is, and I'm posting this here because I have no idea why one should appear here. Every question I can find similar to this is, the answers say that there shouldn't be an NPE and when they run it themselves no such error is detected. I just want to find out why I am getting this error, as it seems like there should be no reason for it.

Sohraub
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    Provide more information about how `gboard` is defined. – Makoto Oct 01 '16 at 18:50
  • Do you think you can un-mark this as a duplicate now? Or at least tell me what else I can do to clarify that it's not. – Sohraub Oct 01 '16 at 19:12
  • What about the implementation of those set methods? – Makoto Oct 01 '16 at 19:19
  • Done. Anything else? – Sohraub Oct 01 '16 at 19:25
  • I'm still tempted to leave this closed; it is the case that `gboard` is `null` since you're redefining it in your constructor (which shadows your variable). The duplicate isn't perfect, so if any gold-badge Java user sees this, my hope is that they find a better one. – Makoto Oct 01 '16 at 21:39
  • If you admit the duplicate is perfect, then why leave it closed? If someone finds an actual duplicate then I'll gladly close it myself, but you just admitted that it's not and it's a problem I could really use some help with. I just don't understand the harm in letting other people see it I guess, I'm just looking for some help. – Sohraub Oct 02 '16 at 18:27

0 Answers0