Last clicked image in array - arrays

Question

I have an array of images, when i click on one of them, I want it to loop and create a pattern. (This part already works). When i want to get the last clicked image out of my array i get a 'NullPointerException'
PImage[] patronen = new PImage[7];
int pLength = patronen.length;
PImage selectedPatroon = patronen[patronen.length-1];
void setup(){
size(1024, 768);
}
void draw(){
createPGrid();
image(selectedPatroon, xPos, yPos);
}
void createPGrid(){
for(int j = 0; j < gpLength; j++){
// Grid maanmaken
xPos = xOffset + ((j % cols) * (size+padding));
yPos = yOffset + ((j / cols) * (size+padding));
// Thumbs
patronen[j] = loadImage( j + ".png");
image(patronen[j], xPos, yPos);
// Check if thumb is clicked
if((mouseX >= xPos && mouseX <= xPos+size) &&
(mouseY >= yPos && mouseY <= yPos+size)){
if (mousePressed){
// grid patronen
xPos = 0;
yPos = 0;
// Loop pattern
while( yPos < height ){
while( xPos < width ){
patronen[j] = loadImage(j + "groot" + ".png");
selectedPatroon = patronen[j]
xPos += 500;
}
yPos +=500;
xPos = 0;
}
rect(xPos, yPos, size, size);
}
}
}
}
EDIT: The thing is, it works perfectly without
PImage selectedPatroon = patronen[patronen.length-1];
but then the looped pattern comes above all my others functions. And i want it to be under that.

Answer 1

You are creating an array at the top of your code then setting an image to the last element in the array, but you're not populating the array first.
PImage[] patronen = new PImage[7]; <<< Blank 7 element array.
int pLength = patronen.length;
PImage selectedPatroon = patronen[patronen.length-1];

Answer 2

To answer the questions you've put in the comments, you cannot populate an array of PImages with ints, those are different variable types. Try something like this in setup():
PImage patronen = new PImage[7];
for(int i = 0; i < patronen.length; i++){
patronen[i] = loadImage("image" + i + ".png"); // or whatever format your filenames are
}
The loadImage(String name) function returns a PImage, so you can insert it directly into your array. Just trying to insert the numbers won't work because the computer doesn't know that the numbers represent the filename without you telling it with loadImage().