Access ArrayList populated in one class, in another class

Question

I have a class called World that has an ArrayList called entities, the data is then added to the list and displayed on the map. The ArrayList needs accessible from another class called Player that also needs to iterate through the list to be able to check if the is intersecting it. What I want to know is how to make the entities ArrayList accessible to the Player class.

the list in the World.java is

public List<Entity> entities; // contains all entities

the ArrayList is being initialized in World.java

entities = new ArrayList<Entity>();// initialise list to new array list

data being hardcoded into this list in World.java

Transform r1 = new Transform();
r1.position.x = 4;
r1.position.y = -4;

Transform r2 = new Transform();
r2.position.x = 5;
r2.position.y = -7;

Transform r3 = new Transform();
r3.position.x = 11;
r3.position.y = -12;

Transform r4 = new Transform();
r4.position.x = 10;
r4.position.y = -8;

Transform t1 = new Transform();
t1.position.x = 3;
t1.position.y = -7;

Transform t2 = new Transform();
t2.position.x = 5;
t2.position.y = -5;

Transform t3 = new Transform();
t3.position.x = 13;
t3.position.y = -13;

Transform t4 = new Transform();
t4.position.x = 7;
t4.position.y = -5;

Transform t5 = new Transform();
t4.position.x = 8;
t4.position.y = -9;

Transform t6 = new Transform();
t4.position.x = 14;
t4.position.y = -14;

entities.add(new Player(new Transform()));// add entity player

entities.add(new Rock(r1));// add entity rock
entities.add(new Rock(r3));// add entity rock

entities.add(new Rock(r2));// add entity rock

entities.add(new Rock(r4));// add entity rock

entities.add(new Tree(t1));// add entity rock
entities.add(new Tree(t3));// add entity rock

entities.add(new Tree(t2));// add entity rock

entities.add(new Tree(t4));// add entity rock

entities.add(new Tree(t5));// add entity rock

entities.add(new Tree(t6));// add entity rock

the list being iterated in World.java

for (Entity entity : entities) {// itaarate through all the entities in list of entities
    entity.render(shader, camera, this);// render each entity
    if (!entity.isActive())
        entities.remove(entity);


}

Player.java class

public class Player extends Entity {

    public ArrayList<Entity> entities; // contains all entities
    public static final int IDLE = 0;
    public static final int RUN = 1;

    public Player(Transform transform) {
        super(4, transform);
        // number of images, fps, file
        setAnimation(IDLE, new Animations(4, 2, "player/idle"));// player standing
        setAnimation(RUN, new Animations(4, 4, "player/run"));// player walking

    }

    @Override
    public void update(float delta, Window window, Camera camera, World world) {
        Vector2f movement = new Vector2f();// gets new position

        if (window.getInput().isKeyDown(GLFW.GLFW_KEY_A))
            movement.add(-10 * delta, 0);// move character 10 units fr every frame

        if (window.getInput().isKeyDown(GLFW.GLFW_KEY_D))
            movement.add(10 * delta, 0);// move character 10 units fr every frame
        if (window.getInput().isKeyDown(GLFW.GLFW_KEY_W))
            movement.add(0, 10 * delta);// move character 10 units fr every frame

        if (window.getInput().isKeyDown(GLFW.GLFW_KEY_S))
            movement.add(0, -10 * delta);// move character 10 units fr every frame


        Rectangle cb = new Rectangle();
        Rectangle ar = new Rectangle();
        int arSize = 20;
        ar.width = arSize;
        ar.height = arSize;

        if (window.getInput().isKeyDown(GLFW.GLFW_KEY_UP))
            ar.x = cb.x + cb.width / 2 - arSize / 2;
        ar.y = cb.y - arSize;

        if (window.getInput().isKeyDown(GLFW.GLFW_KEY_DOWN))
            ar.x = cb.x + cb.width / 2 - arSize / 2;
        ar.y = cb.y + cb.height;

        if (window.getInput().isKeyDown(GLFW.GLFW_KEY_LEFT))
            ar.x = cb.x - arSize;
        ar.y = cb.y + cb.height / 2 - arSize / 2;

        if (window.getInput().isKeyDown(GLFW.GLFW_KEY_RIGHT))
            ar.x = cb.x + cb.width;
        ar.y = cb.y + cb.height / 2 - arSize / 2;

        for (Entity entity : ) {// itaarate through all the entities in list of entities

        }

        move(movement);
        if (movement.x != 0 || movement.y != 0)
            useAnimation(RUN);
        else
            useAnimation(IDLE);

        camera.getPosition().lerp(transform.position.mul(-world.getScale(), new Vector3f()), 0.1f);// follows the player
    }
}

Answer 1

for example say this is your world class has arraylist in it

class World{
private static ArrayList<Entry> list = new ArrayList<>();
list.put(someting);
list.put(someting);
public static ArrayList<Entry> getList(){ // create static method to access list from other class 
 return list;
}

Now from class Player

ArrayList<Entry> list = Wordl.getList();  // you have the list from world class

Answer 2

从阅读评论我只需要使列表静态

Static public List<Entity> entities; // contains all entities

Answer 3

A World object could be composed of many Entity objects. a Player object should not necessarily be composed of the World object. Instead when a Player needs to know about the World, or entities in the world, it should be accessible, for example;

class Entity {

    void update() {

    }

    void update(Entity other) {

    }

}

class World {

    private final List<Entity> entities;

    public World(List<Entity> entities) {
        this.entities = entities;
    }

    public void update() {
        for (Entity entity : entities) {
            entity.update();

            for (Entity other : entities) {
                if (entity == other) {
                    continue;
                }
                update(entity, other);
            }
        }
    }

    public void update(Entity source, Entity target) {
        source.update(target);
    }

}