Reducing the number of collide methods in a Java Game

Question

I'm making a simple game in java, and I have many methods which test if two object collide. Objects include a man, enemy, arrow, wall, coin and so on. I have a bunch of methods which count for every type of collision which could occur, they look like this:

    public boolean collide(Arrow a, Enemy b)
    {
        Rectangle a1 = a.getBounds();
        Rectangle b1 = b.getBounds();
        if(a1.intersects(b1)) return true;
        else return false;
    }

Is there away to create a generic method? I tried using object a and object b as the arguments but the compiler compained it couldn't find getBounds() for the objects.

Use a common interface of those classes instead of `Object`. That interface must contain a method `Rectangle getBounds();` and those classes must implement it. Also, you can replace the last two lines with `return a1.intersects(b1);` — jlordo, Mar 09 '13 at 16:09
See [this answer](http://stackoverflow.com/a/14575043/418556) for an example of collision detection using `Shape` instances. — Andrew Thompson, Mar 09 '13 at 16:23

score 3 · Accepted Answer · answered Mar 09 '13 at 16:12

3

You can do something like :

public boolean collide(HasBounds a, HasBounds b){...

With the interface :

public interface HasBounds{
  Rectangle getBounds();
}

That you should define on your objects Arrow,Enemy etc... (you may already have an object hierarchy suitable for that).

answered Mar 09 '13 at 16:12

benzonico

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even simpler: `public boolean collide(HasBounds a, HasBounds b){` – jlordo Mar 09 '13 at 16:13

score 1 · Answer 2 · answered Mar 09 '13 at 16:15

what do you think of this..

 public boolean collide(Rectangle a1, Rectangle b1)
 {
        return a1.intersects(b1);
 }

or may be Create an interface

public interface CanCollide {
   Rectangle getBounds();
}

and use it in the method...

 public boolean collide(CanCollide a, CanCollide b)
 {
     Rectangle a1 = a.getBounds();
     Rectangle b1 = b.getBounds();
     if(a1.intersects(b1)) return true;
     else return false;
 }

Hope you find it usefull.

Thanks!

@leo.

score -1 · Answer 3 · answered Mar 09 '13 at 16:14

-1

Just make abstract class GameObject with method: Rectangle2D getShape(). This method could look like:

abstract class GameObject {
    private Image image;

    GameObject(String path) {
        try {
          image = ImageIO.read(new File(path));
        } catch (IOException ex) {}
    }

    Rectangle2D getShape() {
       return new Rectangle2D.Float(0, 0, (int)image.getWidth(), (int)image.getHeight());
    }
}

Player, Enemy, Arrow, Wall would be subclasses of GameObject class

answered Mar 09 '13 at 16:14

Michał Tabor

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And how does this reduce the number of `collide()` methods? – jlordo Mar 09 '13 at 16:17
Now you don't need to overload collide() method with different collids modifications. Instead there is one method width parameters: (GameObject collid1, GameObject collid2) – Michał Tabor Mar 09 '13 at 16:19
That should be part of the answer. The constructor and `getShape()` methods have nothing to with OPs problem.. – jlordo Mar 09 '13 at 16:20

Reducing the number of collide methods in a Java Game

3 Answers3