Question

I made a program that uses a 2D array to draw a grid, but I am getting a null pointer exception. Here is my code:

Cell[][] Cells;
void setup(){
  size(500,500);
  background(255);
  for (int x = 0; x < 50; x++) {
    for (int y = 0; y < 50; y++) {
      Cells[x][y] = new Cell(round(random(255)),x * 10,y * 10,10,10);
    }
  }
}
void draw(){
  for (int x = 0; x < 50; x++) {
    for (int y = 0; y < 50; y++) {
      Cells[x][y].Draw();
    }
  }
}
class Cell{
  int X;
  int Y;
  int Width;
  int Height;
  int Color;
  Cell(int C,int X,int Y,int Width,int Height){
    Color = C;
    X = X;
    Y = Y;
    Width = Width;
    Height = Height;
  }
  void Draw(){
    fill(Color);
    rect(X,Y,Width,Height);
  }
}

and here is the error message:

Exception in thread "Animation Thread" java.lang.NullPointerException
    at Grid.setup(Grid.java:27)
    at processing.core.PApplet.handleDraw(PApplet.java:2103)
    at processing.core.PGraphicsJava2D.requestDraw(PGraphicsJava2D.java:190)
    at processing.core.PApplet.run(PApplet.java:2006)
    at java.lang.Thread.run(Thread.java:662)

what am I doing wrong?

Answer 1

You missed to create the array:

Cell[][] cells = new Cell[50][50];