Java中两个对象之间的碰撞检测

Question

I'm really struggling detecting collision between two Car objects of Car class. The code is pretty long so its hard to include it all. I've included my collision method. If you can spot any logic errors with it which I'm thinking is my issue that'd be great. If you need more context I asked an earlier similar question which includes a lot more of the code here , but i still dont have a solution..

What i want it to do is tell me when two cars are touching. What it's doing is nothing but printing 'no collision' even when there are collisions.

collision method (inside environment class) -

public boolean collision() {

    double MIN_DIS = 0.1;
    for (Car a : cars) {
        for (Car b : cars) {
            if (!(a.equals(b)) && (Math.abs(a.getPosition() - b.getPosition()) < MIN_DIS)) {
                return true;
            }
        }
    }
    return false;
}

Calling method (inside main where i add cars) -

    if(e.collision() == true) {
        System.out.println("collision");
    } else {
        System.out.println("no collision");
    } 

Equals method (i decided to use !(a == b) for now though) -

public boolean equals(Object obj) {
    if (obj instanceof Car){
        Car car = (Car) obj;
        return car.getPosition() == this.position && car.getLane() == this.lane && car.getColor().equals(this.color) && car.getSpeed() == this.speed; 
    }
    return false;
}

Answer 1

You may want to change the detection 'range'. If you look at the way you're detecting your cars, you're only looking for the co-ordinate that the sprite/vector is positioned at which is going to be relatively hard for them to collide if there are more than a few pixels. Try finding the position of Car A from the width/length of Car B .

Answer 2

I think that the equality method is not correct. And it causes some collision detection problems. We can not assume that two Car with the same property are the same object. For example:

e.add(new Car(  0, 63, 2, new Color(1.0f,1.0f,1.0f, 1.0)));
e.add(new Car(  0, 63, 2, new Color(1.0f,1.0f,1.0f, 1.0)));

In this case there is a collision but it would never be detected since the two objects, through the equals method implemented, are the same.

In contexts like this, game engine or modelling system, it is useful to differentiate each object in your world with an ID, as each instance is unique.

Moreover as @Jason say, to correctly capture a collision you have to compute the length or the width of the object.