Compute the overall area of some rectangles...

RectsArea.java

public class RectsArea {
    public static long area(java.awt.Rectangle... rects) {
        if (rects == null)
            return 0;
        java.awt.Rectangle massArea = null;
        for (java.awt.Rectangle r : rects)
            if (massArea == null)
                massArea = r;
            else
                massArea = massArea.union(r);
        if (massArea == null)
            return 0;
        if (massArea.x < 0) {
            int moved = 0 - massArea.x;
            massArea.x = 0;
            for (java.awt.Rectangle r : rects)
                r.x += moved;
        }
        if (massArea.y < 0) {
            int moved = 0 - massArea.y;
            massArea.y = 0;
            for (java.awt.Rectangle r : rects)
                r.y += moved;
        }
        java.awt.image.BufferedImage map = new java.awt.image.BufferedImage(massArea.width, massArea.height, java.awt.image.BufferedImage.TYPE_INT_ARGB);
        java.awt.Graphics g = map.createGraphics();
        java.awt.Color brush = new java.awt.Color(0, 0, 0, 1);
        g.setColor(brush);
        for (java.awt.Rectangle r : rects)
            g.fillRect(r.x, r.y, r.width, r.height);
        g.dispose();
        long area = 0;
        for (int x = 0; x < map.getWidth(); ++x)
            for (int y = 0; y < map.getHeight(); ++y)
                if (new java.awt.Color(map.getRGB(x, y)).equals(brush))
                    ++area;
        return area;
    }
}