Issue with using arrays in java?

Question

So, I have a class Square and I am trying to use an array for it board. Here is my code:

public class Square{
   public int pcolor;
   public int contains;
   public int xPos;
   public int yPos;
   Square(int xp,int yp,int pc,int cont){
       xPos=xp;
       yPos=yp;
       contains=cont;
       pcolor=pc;
   }
};
Square[] board = new Square[64];
board[0].xPos=0;

This gives me unexpected token: [ on board[0].xpos=0;. Can anyone help me resolve this?

EDIT:

OK, I moved board[0].xpos=0; inside a method; now it gives me NullPointerException. What do I do?

The error is on a different line, please post more of your code. — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Feb 24, 2012 at 14:00
This is not the full code then. Anyone who will compile this will get a compile-time error that the statements on the bottom are unexpected (they need to be in a method in the same or different class. And then get a run-time null pointer exception that you are not setting each array value to a new Square object. — jn1kk
– jn1kk, Commented Feb 24, 2012 at 14:30
For your edit initialize every value to a new object. board[0] = new Square(num, num, num, num); — jn1kk
– jn1kk, Commented Feb 24, 2012 at 15:23

amit · Accepted Answer · 2012-02-24 14:30:20Z

3

You are trying to make a statement not inside a method or a static scope.

The statement board[0].xPos = 0; should [probably] be inside a method.

You also seem to have a redundant };

This code compiles just fine:

public class Square{
    public int pcolor;
    public int contains;
    public int xPos;
    public int yPos;
    Square(int xp,int yp,int pc,int cont){
        xPos=xp;
        yPos=yp;
        contains=cont;
        pcolor=pc;
    }
    Square[] board = new Square[64];
}

To initialize [and access] elements in board - you will have to do it in a method or in the constructor.

edited Feb 24, 2012 at 14:30

answered Feb 24, 2012 at 14:23

amit

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8 Comments

user1188752 Over a year ago

Why is Square[] board inside of class Square

amit Over a year ago

@user1188752: I have no idea what you are actually trying to do. It is just a sample of a code that is compiling. Without more information on what you are trying to achieve - I could only guess.

user1188752 Over a year ago

Chess game in Processing - Square is one square on the board

amit Over a year ago

@user1188752 Then Square[] board should probably be inside a Game class or something indeed. Now that you have solved the compilation error - note that Square[] board = new Square[64]; does not create Squares. It only create the array, holding nulls. You will need to initialize board[i] = new Square(...); for each i.

amit Over a year ago

@user1188752: Try to "play with it", and see if you can figure it out. If not - avoid editting this question with new issues - you should post a new question - describing the new situation and the new problem. I am sure someone will answer you pretty quickly...

|

invariant · Accepted Answer · 2012-02-24 14:10:20Z

1

Well, if you do this correctly you will get NullPointerException because you didn't create any object yet. My guess is you did some syntax error.

edited Feb 24, 2012 at 14:10

user647772

answered Feb 24, 2012 at 14:04

invariant

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4 Comments

user1188752 Over a year ago

What do you mean, "you didn't create any object yet"?

jn1kk Over a year ago

@amit I am thinking he might be using an IDE which would pre-process the syntax since he might have put the statements outside of a method.

amit Over a year ago

@skynorth: I don't think so, I think that the fact that the statements are not in a method - caused the compilation error - as expected.

jn1kk Over a year ago

@amit the fact that he got unexpected token compilation error tells me that he is using a custom IDE (and not even real Java, see his above comment). The Java compiler would never give that kind of compilation error.

Marsellus Wallace · Accepted Answer · 2012-02-24 14:59:34Z

0

All the Squares in board are null and you're trying to access a field of a null Object...

You can initialize the array with:

for(int i = 0; i < board.length; i++)
    board[i] = new Square(...something_here...);

Also, I'm not sure what you're trying to do, but you should consider using a Square[][]!

answered Feb 24, 2012 at 14:59

Marsellus Wallace

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