如何优化此代码，使圆形数组的轮廓显示？

Question

I have an array of a Unit object and the unit object has center cx, cy, and radius cr. I want just the outline of the circles to show (think a ven diagram without the overlapping bits). I managed to do it, but it makes it extremely slow as it is a nested for loop. Here is the code:

(this is all in a method that cycles through all the units)

  ArrayList<Integer> validangles = new ArrayList<Integer>();

  public void getValidAngles(ArrayList<Unit> units) { //get all the angles that aren't overlapping
    ArrayList<Integer> invalidAngles = new ArrayList<Integer>();
    for (int i = 0; i < units.size(); i++) { //cycle through all other units
        Unit c2 = units.get(i);
        if (this != c2) { //make sure it is not the same unit
            for (int ia = 0; ia < 360; ia += 10) { //cycle through the angles
                double ca = Math.toRadians(ia);
                Point p = new Point( //point on the circle
                        (int) Math.round((c2.getCx() + (cr * Math.cos(ca)))),
                        (int) Math.round((c2.getCy() + (cr * Math.sin(ca)))));
                if (overlapping(p)) {
                    invalidAngles.add(ia-180); //this angle should not be shown
                }
            }
        }

    }
    validangles.clear();
    for (int i = 0; i < 360; i += 10) {
        if (!invalidAngles.contains(i-180)) {
            validangles.add(i-180);
        }

    }
}

public void drawValidAngles(Graphics g2) {

    for(int i : validangles) {
        int x = (int)Math.round(cx+cr*Math.cos(Math.toRadians(i)));
        int y = (int)Math.round(cy+cr*Math.sin(Math.toRadians(i)));
        g2.drawLine(x, y, x, y);
    }
}

The issue is that if I have upwards of a couple hundred units, which will be common, it slows the program down a ton because of nesting a forloop of units in another forloop of units.

Answer 1

You can use Area class to combine ellipses (each ellipse represents the Unit shape). Eg

    Shape s=new Ellipse2D.Float(10,10,200,100);
    Area a=new Area(new Ellipse2D.Float(150,20,100,200));
    a.add(new Area(s));

Then you can use the sum Area as outline. See working example here