How to call function of an Array in ArrayList? Java

Question

I'm want to create an ArrayList that contains an Array and call the function of the objects inside that array.

I'm trying to call the function display() inside of the Array but I'm getting a NPE even though the array contains an object.

this is my code:

class Ball
{
  int x;
  int y;
  int size;
  color c;

  Ball()
  {
    x = int (random(width));
    y = int (random(height));
    size = int (random(100));
    c = color(random(255));
  }

  void display()
  {
    fill(c);
    ellipse(x,y,size,size);
  }
}

ArrayList<Ball[]> balls;


void setup()
{
  size(500,500);

  balls = new ArrayList<Ball[]>();

  for( int i = 0; i < 1; i++)
  {
    balls.add(new Ball[2]);
    println(balls);
  }
}

void draw()
{
  background(255);

  for( int i = 0; i < 1; i++)
  {
    Ball[] b = balls.get(i);
    b[i].display();
  }
}

does anybody know how to do this?

Your problem is that you're not creating any Balls - only an empty array. — Dawood ibn Kareem
– Dawood ibn Kareem, Commented Apr 28, 2016 at 21:01
The array does not contain a non-null object reference. Even though you clearly stated that it did in English, you didn't enforce that in Java. Since the compiler only reacts to the Java source, you will need to reflect your assertion in your code. — Lew Bloch
– Lew Bloch, Commented Apr 28, 2016 at 21:59

Reut Sharabani · Accepted Answer · 2016-04-28 21:02:56Z

1

You have a list of empty Ball arrays. Add balls after creating the (empty) array:

void setup()
{
  size(500,500);

  balls = new ArrayList<Ball[]>();

  for( int i = 0; i < 1; i++)
  {
    Ball[] ballsArray = new Ball[2];
    ballsArray[0] = new Ball();
    ballsArray[1] = new Ball();
    balls.add(ballsArray);
    println(balls);
  }
}

answered Apr 28, 2016 at 21:02

Reut Sharabani

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