I am trying to implement grid-based collision in a 2d game with moving circles. The canvas is 400x400 pixels. Below you can see the code for my Grid class. What I want it to do is check inside which box the entities are located and then run a collision check if there are 2 or more entities in the same box. Right now I do not know how to find the position of an entity in a specific box. I know there are many tutorials online, but I haven't been able to find an answer to my question, because they are either written in C/C++ or use the 2d array approach. Code snippets and other help is greatly appreciated. Thanks. public class Grid { ArrayList<ArrayList<Entity>> boxes = new ArrayList<>(); double boxSize = 40; double boxesAmount = 10; ... ... public void checkBoxLocation(ArrayList<Entity> entities) { for (int i = 0; i < entities.size(); i++) { // Get top left coordinates of each entity double entityLeft = entities.get(i).getLayoutX() - entities.get(i).getRadius(); double entityTop = entities.get(i).getLayoutY() + entities.get(i).getRadius(); // Divide coordinate by box size to find the approximate location of the entity for (int j = 0; j < boxesAmount; j++) { //Select each box if ((entityLeft / boxSize <= j + 0.7) && (entityLeft / boxSize >= j)) { if ((entityTop / boxSize <= j + 0.7) && (entityTop / boxSize >= j)) { holdingBoxes.get(j).add(entities.get(i)); System.out.println("Entity " + entities.get(i) + " added to box " + j); } } } } } }