Extracting an image from an array in Processing - arrays

Question

Does anyone have any suggestions on what might be going wrong with this code? I'm trying to load tiles of images into a large array and then display them. Later on I'll shuffle the pieces. The issue I'm running into is seen near the bottom. I have a for loop that should plug the value of i into the output array and display the relevant image at that index value. Instead I get a null pointer exception. If I replace the letter i with an integer it works perfectly. What could be preventing processing from passing that value if i into the array? Any thoughts? Thanks.
int tileSize = 100;
PImage out; PImage sample;
PImage img;
PImage img2;
String[] imageNames = {"arctic_fox.jpg", "bbridge_in_the_am.jpg", "Kali2.jpg"};
PImage[] images = new PImage[imageNames.length];
//PImage[] output = new PImage[((1440/tileSize)*imageNames.length)*(900/tileSize)];
PImage[] output = new PImage[2000];
int tintScale = 200;
void setup() {
fullScreen();
for (int i=0; i < imageNames.length; i++) {
String imageName = imageNames[i];
images[i] = loadImage(imageName);
}
out = createImage(width, height, RGB);
noLoop();
println("test");
}
void draw() {
background(0);
println(width, height);
println(output.length);
int counter=0;
for (int i = 0; i < imageNames.length; i++) {
img = loadImage(imageNames[i]);
img.resize(0,900);
for (int y=0; y<img.height; y+=tileSize) {
for (int x=0; x<img.width; x+=tileSize/3) {
sample = img.get(x, y, tileSize, tileSize);
output[counter] = sample;
tint(255, tintScale);
counter++;
//println(counter);
//image(out, random(0, width-img_x), random(0, height-img_y));
}
//image(output[i],30,30);
}
}
for (int i=0;i<output.length;i++){
image(output[30],i*tileSize,i*tileSize);
}
//for (int y=0; y<out.height; y+=tileSize) {
// for (int x=0; x<out.width; x+=tileSize) {
// i = 800;
// //tint(255, tintScale);
// image(output[i], x, y);
// }
//}
}

Answer 1

I hope you solved it, but this is the problem:
PImage[] output = new PImage[2000];
You are initializing the array with 2000 null values, and then enter less then 300 tiles. That's why you get a null pointer error. You have to calculate how large your array will be before you initialize it. Or perhaps better, use an arraylist:
ArrayList<PImage> output = new ArrayList<PImage>();
//to add a tile:
output.add(sample);
//to draw all tile:
for(int i = 0; i< output.size();i++)
{
image(output[i],i*tileSize,i*tileSize);
}
You can read more about arraylists here
Final note: as Kevin Workman says, loadImage() and this process of dividing into tiles does not belong in 'void draw()'. It should be in setup() or in a separate function, called from setup().